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[apple/xnu.git] / bsd / man / man2 / getattrlist.2

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.\"     @(#)getattrlist.2
.
.Dd October 14, 2004
.Dt GETATTRLIST 2
.Os Darwin
.Sh NAME
.Nm getattrlist
.Nd get file system attributes
.Sh SYNOPSIS
.Fd #include <sys/attr.h>
.Fd #include <unistd.h>
.Ft int
.Fn getattrlist "const char* path" "struct attrlist * attrList" "void * attrBuf" "size_t attrBufSize" "unsigned long options"
.
.Sh DESCRIPTION
The
.Fn getattrlist
function returns attributes (that is, metadata) of file system objects.
You can think of 
.Fn getattrlist
as a seriously enhanced version of
.Xr stat 2 .
The function returns attributes about the file system object specified by 
.Fa path
in the buffer specified by 
.Fa attrBuf
and
.Fa attrBufSize .
The 
.Fa attrList 
parameter determines what attributes are returned. 
The 
.Fa options 
parameter lets you control specific aspects of the function's behaviour.
.Pp
.
The 
.Fn getattrlist 
function is only supported by certain volume format implementations. 
For maximum compatibility, client programs should use high-level APIs 
(such as the Carbon File Manager) to access file system attributes.
These high-level APIs include logic to emulate file system attributes 
on volumes that don't support 
.Fn getattrlist .
.Pp
.
Not all volumes support all attributes.
See the discussion of 
.Dv ATTR_VOL_ATTRIBUTES 
for a discussion of how to determine whether a particular volume supports a 
particular attribute.
.Pp
Furthermore, you should only request the attributes that you need. 
Some attributes are expensive to calculate on some volume formats. 
For example, 
.Dv ATTR_DIR_ENTRYCOUNT 
is usually expensive to calculate on non-HFS [Plus] volumes.
If you don't need a particular attribute, you should not ask for it.
.Pp
.
.\" path parameter
.
The
.Fa path
parameter must reference a valid file system object.
Read, write or execute permission of the object itself is not required, but 
all directories listed in the path name leading to the object must be 
searchable.
.Pp
.
.\" attrList parameter
.
The
.Fa attrList
parameter is a pointer to an 
.Vt attrlist 
structure, as defined by
.Aq Pa sys/attr.h
(shown below).
It determines what attributes are returned by the function.
You are responsible for filling out all fields of this structure before calling the function. 
.Bd -literal
typedef u_int32_t attrgroup_t;
.Pp
struct attrlist {
    u_short     bitmapcount; /* number of attr. bit sets in list */
    u_int16_t   reserved;    /* (to maintain 4-byte alignment) */
    attrgroup_t commonattr;  /* common attribute group */
    attrgroup_t volattr;     /* volume attribute group */
    attrgroup_t dirattr;     /* directory attribute group */
    attrgroup_t fileattr;    /* file attribute group */
    attrgroup_t forkattr;    /* fork attribute group */
};
#define ATTR_BIT_MAP_COUNT 5
.Ed
.Pp
.
.\" attrlist elements
.
The fields of the 
.Vt attrlist
structure are defined as follows.
.Bl -tag -width XXXbitmapcount
.
.It bitmapcount
Number of attribute bit sets in the structure.
In current systems you must set this to 
.Dv ATTR_BIT_MAP_COUNT .
.
.It reserved
Reserved.
You must set this to 0.
.
.It commonattr
A bit set that specifies the common attributes that you require.
Common attributes relate to all types of file system objects. 
See below for a description of these attributes.
.
.It volattr
A bit set that specifies the volume attributes that you require.
Volume attributes relate to volumes (that is, mounted file systems).
See below for a description of these attributes.
If you request volume attributes, 
.Fa path
must reference the root of a volume.
In addition, you can't request volume attributes if you also request 
file or directory attributes.
.
.It dirattr
A bit set that specifies the directory attributes that you require.
See below for a description of these attributes.
.
.It fileattr
A bit set that specifies the file attributes that you require.
See below for a description of these attributes.
.
.It forkattr
A bit set that specifies the fork attributes that you require.
Fork attributes relate to the actual data in the file, 
which can be held in multiple named contiguous ranges, or forks.
See below for a description of these attributes.
.
.El
.Pp
.
Unless otherwise noted in the lists below, attributes are read-only. 
Attributes labelled as read/write can be set using 
.Xr setattrlist 2 .
.Pp
.
.\" attrBuf and attrBufSize parameters
.
The
.Fa attrBuf
and 
.Fa attrBufSize
parameters specify a buffer into which the function places attribute values. 
The format of this buffer is sufficiently complex that its description 
requires a separate section (see below).
The initial contents of this buffer are ignored.
.Pp
.
.\" option parameter
.
The
.Fa options
parameter is a bit set that controls the behaviour of
.Fn getattrlist .
The following option bits are defined.
.
.Bl -tag -width XXXbitmapcount
.
.It FSOPT_NOFOLLOW
If this bit is set, 
.Fn getattrlist 
will not follow a symlink if it occurs as 
the last component of
.Fa path .
.
.El
.
.Sh ATTRIBUTE BUFFER
.
The data returned in the buffer described by 
.Fa attrBuf 
and 
.Fa attrBufSize 
is formatted as follows.
.Pp
.
.Bl -enum
.
.It
The first element of the buffer is a 
.Vt unsigned long 
that contains the overall length, in bytes, of the attributes returned. 
This size includes the length field itself. 
.
.It
Following the length field is a list of attributes. 
Each attribute is represented by a field of its type, 
where the type is given as part of the attribute description (below). 
.
.It
The attributes are placed into the attribute buffer in the order 
that they are described below.
.
.El
.Pp
.
If the attribute is of variable length, it is represented 
in the list by an 
.Vt attrreference 
structure, as defined by 
.Aq Pa sys/attr.h
(shown below).
.
.Bd -literal
typedef struct attrreference {
    long        attr_dataoffset;
    size_t      attr_length;
} attrreference_t;
.Ed
.Pp
.
This structure contains a 'pointer' to the variable length attribute data.
The 
.Fa attr_length 
field is the length of the attribute data (in bytes). 
The 
.Fa attr_dataoffset 
field is the offset in bytes from the 
.Vt attrreference 
structure 
to the attribute data. 
This offset will always be a multiple of sizeof(unsigned long) bytes, 
so you can safely access common data types without fear of alignment 
exceptions.
.Pp
.
The 
.Fn getattrlist 
function will silently truncate attribute data if 
.Fa attrBufSize 
is too small. 
The length field at the front of the attribute list always represents 
the length of the data actually copied into the attribute buffer. 
If the data is truncated, there is no easy way to determine the 
buffer size that's required to get all of the requested attributes. 
You should always pass an 
.Fa attrBufSize 
that is large enough to accommodate the known size of the attributes 
in the attribute list (including the leading length field).
.Pp
.
Because the returned attributes are simply truncated if the buffer is 
too small, it's possible for a variable length attribute to reference 
data beyond the end of the attribute buffer.  That is, it's possible 
for the attribute data to start beyond the end of the attribute buffer 
(that is, if 
.Fa attrRef 
is a pointer to the 
.Vt attrreference_t ,
( ( (char *) 
.Fa attrRef 
) + 
.Fa attr_dataoffset 
) > ( ( (char *) 
.Fa attrBuf 
) + 
.Fa attrSize 
) ) or, indeed, for the attribute data to extend beyond the end of the attribute buffer (that is, 
( ( (char *) 
.Fa attrRef 
) + 
.Fa attr_dataoffset 
+ 
.Fa attr_datalength 
) > ( ( (char *) 
.Fa attrBuf 
) + 
.Fa attrSize 
) ).
If this happens you must increase the size of the buffer and call 
.Fn getattrlist 
to get an accurate copy of the attribute.
.
.Sh COMMON ATTRIBUTES
.
Common attributes relate to all types of file system objects.
The following common attributes are defined.
.
.Bl -tag -width ATTR_VOL_ALLOCATIONCLUMP
.
.It ATTR_CMN_NAME
An 
.Vt attrreference 
structure containing the name of the file system object as 
UTF-8 encoded, null terminated C string.
The attribute data length will not be greater than 
.Dv NAME_MAX + 
1.
.Pp
.
.It ATTR_CMN_DEVID
A 
.Vt dev_t 
containing the device number of the device on which this 
file system object's volume is mounted.
Equivalent to the 
.Fa st_dev 
field of the 
.Vt stat 
structure returned by 
.Xr stat 2 .
.
.It ATTR_CMN_FSID
An 
.Vt fsid_t 
structure containing the file system identifier for the volume on which 
the file system object resides.
Equivalent to the 
.Fa f_fsid 
field of the 
.Vt statfs 
structure returned by 
.Xr statfs 2 .
.
.Pp
This value is not related to the file system ID from traditional Mac OS (for example, 
the 
.Fa filesystemID 
field of the 
.Vt FSVolumeInfo
structure returned by Carbon's FSGetVolumeInfo() function).
On current versions of Mac OS X that value is synthesised by the Carbon File Manager.
.
.It ATTR_CMN_OBJTYPE
An 
.Vt fsobj_type_t 
that identifies the type of file system object. 
The values are taken from 
.Vt enum vtype 
in 
.Aq Pa sys/vnode.h .
.
.It ATTR_CMN_OBJTAG
An 
.Vt fsobj_tag_t 
that identifies the type of file system containing the object.
The values are taken from 
.Vt enum vtagtype 
in
.Aq Pa sys/vnode.h .
.
.It ATTR_CMN_OBJID
An 
.Vt fsobj_id_t 
structure that uniquely identifies the file system object 
within its volume.
The fid_generation field of this structure will be zero for all non-root callers
(effective UID not 0).
This identifier need not be persistent across an unmount/mount sequence.
.Pp
.
Some volume formats use well known values for the 
.Fa fid_objno 
field for the root directory (2) and the parent of root directory (1). 
This is not a required behaviour of this attribute.
.
.It ATTR_CMN_OBJPERMANENTID
An 
.Vt fsobj_id_t 
structure that uniquely identifies the file system object 
within its volume.
The fid_generation field of this structure will be zero for all non-root callers
(effective UID not 0).
This identifier should be persistent across an unmount/mount sequence.
.Pp
Some file systems (for example, original HFS) may need to modify the on-disk 
structure to return a persistent identifier. 
If such a file system is mounted read-only, an attempt to get this attribute 
will fail with the error 
.Dv EROFS .
.
.It ATTR_CMN_PAROBJID
An 
.Vt fsobj_id_t 
structure that identifies the parent directory of the file system object. 
The fid_generation field of this structure will be zero for all non-root callers 
(effective UID not 0).
Equivalent to the ATTR_CMN_OBJID attribute of the parent directory.
This identifier need not be persistent across an unmount/mount sequence.
.Pp
.
On a volume that supports hard links, a multiply linked file has no unique parent. 
This attribute will return an unspecified parent.
.Pp
.
For some volume formats this attribute is very expensive to calculate. 
.
.It ATTR_CMN_SCRIPT
(read/write) A 
.Vt text_encoding_t 
containing a text encoding hint for 
the file system object's name. 
It is included to facilitate the lossless round trip conversion of names between 
Unicode and traditional Mac OS script encodings.
The values are defined in 
.Aq Pa CarbonCore/TextCommon.h .
File systems that do not have an appropriate text encoding value should return 
kTextEncodingMacUnicode. 
See DTS Q&A 1173 "File Manager Text Encoding Hints".
.
.It ATTR_CMN_CRTIME
(read/write) A 
.Vt timespec 
structure containing the time that the file system object 
was created. 
.
.It ATTR_CMN_MODTIME
(read/write) A 
.Vt timespec 
structure containing the time that the file system object 
was last modified. 
Equivalent to the 
.Fa st_mtimespec 
field of the 
.Vt stat 
structure returned by 
.Xr stat 2 .
.
.It ATTR_CMN_CHGTIME
(read/write) A 
.Vt timespec 
structure containing the time that the file system object's 
attributes were last modified. 
Equivalent to the 
.Fa st_ctimespec 
field of the 
.Vt stat 
structure returned by 
.Xr stat 2 .
.
.It ATTR_CMN_ACCTIME
(read/write) A 
.Vt timespec 
structure containing the time that the file system object 
was last accessed. 
Equivalent to the 
.Fa st_atimespec 
field of the 
.Vt stat 
structure returned by 
.Xr stat 2 .
.
.It ATTR_CMN_BKUPTIME
(read/write) A 
.Vt timespec 
structure containing the time that the file system object was 
last backed up. 
This value is for use by backup utilities. 
The file system stores but does not interpret the value.
.
.It ATTR_CMN_FNDRINFO
(read/write) 32 bytes of data for use by the Finder.
Equivalent to the concatenation of a 
.Vt FileInfo 
structure and an 
.Vt ExtendedFileInfo 
structure 
(or, for directories, a 
.Vt FolderInfo 
structure and an 
.Vt ExtendedFolderInfo 
structure).
These structures are defined in 
.Aq Pa CarbonCore/Finder.h .
.Pp
This attribute is not byte swapped by the file system.
The value of multibyte fields on disk is always big endian. 
When running on a little endian system (such as Darwin on x86), 
you must byte swap any multibyte fields.
.
.It ATTR_CMN_OWNERID
(read/write) A 
.Vt uid_t 
containing the owner of the file system object. 
Equivalent to the 
.Fa st_uid 
field of the 
.Vt stat 
structure returned by 
.Xr stat 2 .
.
.It ATTR_CMN_GRPID
(read/write) A 
.Vt gid_t 
containing the group of the file system object. 
Equivalent to the 
.Fa st_gid 
field of the 
.Vt stat 
structure returned by 
.Xr stat 2 .
.
.It ATTR_CMN_ACCESSMASK
(read/write) A 
.Vt mode_t 
containing the access permissions of the file system object. 
Equivalent to the 
.Fa st_mode 
field of the 
.Vt stat 
structure returned by 
.Xr stat 2 .
.
.It ATTR_CMN_NAMEDATTRCOUNT
A 
.Vt unsigned long
containing the number of named attributes of the file system object. 
No built-in file systems on Mac OS X currently support named attributes.
.
.It ATTR_CMN_NAMEDATTRLIST
An 
.Vt attrreference 
structure containing a list of named attributes of the file system object.
No built-in file systems on Mac OS X currently support named attributes.
Because of this, the structure of this attribute's value is not yet defined.
.
.It ATTR_CMN_FLAGS
(read/write) A 
.Vt unsigned long 
containing file flags.
Equivalent to the 
.Fa st_flags 
field of the 
.Vt stat 
structure returned by 
.Xr stat 2 .
For more information about these flags, see 
.Xr chflags 2 .
.Pp
.
The order that attributes are placed into the attribute buffer 
almost invariably matches the order of the attribute mask bit values. 
The exception is 
.Dv ATTR_CMN_FLAGS . 
If its order was based on its bit position, it would be before 
the 
.Dv ATTR_CMN_NAMEDATTRCOUNT 
/ 
.Dv ATTR_CMN_NAMEDATTRLIST 
pair, however, 
it is placed in the buffer after them.
.
.It ATTR_CMN_USERACCESS
A 
.Vt unsigned long
containing the effective permissions of the current user 
(the calling process's effective UID) for this file system object. 
You can test for read, write, and execute permission using 
.Dv R_OK ,
.Dv W_OK ,
and
.Dv X_OK , 
respectively.  See 
.Xr access 2 
for more details.
.
.El
.
.Sh VOLUME ATTRIBUTES
.
Volume attributes relate to volumes (that is, mounted file systems).
The following volume attributes are defined.
.
.Bl -tag -width ATTR_VOL_ALLOCATIONCLUMP
.
.It ATTR_VOL_INFO
For reasons that are not at all obvious, you must set 
.Dv ATTR_VOL_INFO 
in the 
.Fa volattr
field if you request any other volume attributes.
This does not result in any attribute data being added to the attribute buffer.
.
.It ATTR_VOL_FSTYPE
A 
.Vt unsigned long 
containing the file system type.
Equivalent to the 
.Fa f_type 
field of the 
.Vt statfs 
structure returned by 
.Xr statfs 2 .
Generally not a useful value.
.
.It ATTR_VOL_SIGNATURE
A 
.Vt unsigned long 
containing the volume signature word. 
This value is unique within a given file system type and lets you 
distinguish between different volume formats handled by the same file system.
See 
.Aq Pa CarbonCore/Files.h 
for more details.
.
.It ATTR_VOL_SIZE
An 
.Vt off_t
containing the total size of the volume in bytes.
.
.It ATTR_VOL_SPACEFREE
An 
.Vt off_t
containing the free space on the volume in bytes.
.
.It ATTR_VOL_SPACEAVAIL
An 
.Vt off_t
containing the space, in bytes, on the volume available to non-privileged processes. 
This is the free space minus the amount of space reserved by the system to prevent critical 
disk exhaustion errors. 
Non-privileged programs, like a disk management tool, should use this value to display the 
space available to the user.
.Pp
.Dv ATTR_VOL_SPACEAVAIL 
is to 
.Dv ATTR_VOL_SPACEFREE 
as 
.Fa f_bavail 
is to 
.Fa f_bfree 
in 
.Xr statfs 2 .
.
.It ATTR_VOL_MINALLOCATION
An 
.Vt off_t
containing the minimum allocation size on the volume in bytes. 
If you create a file containing one byte, it will consume this much space.
.
.It ATTR_VOL_ALLOCATIONCLUMP
An 
.Vt off_t
containing the allocation clump size on the volume, in bytes. 
As a file is extended, the file system will attempt to allocate 
this much space each time in order to reduce fragmentation.
.
.It ATTR_VOL_IOBLOCKSIZE
A 
.Vt unsigned long 
containing the optimal block size when reading or writing data. 
Equivalent to the 
.Fa f_iosize 
field of the 
.Vt statfs 
structure returned by 
.Xr statfs 2 .
.
.It ATTR_VOL_OBJCOUNT
A 
.Vt unsigned long 
containing the number of file system objects on the volume.
.
.It ATTR_VOL_FILECOUNT
A 
.Vt unsigned long 
containing the number of files on the volume.
.
.It ATTR_VOL_DIRCOUNT
A 
.Vt unsigned long 
containing the number of directories on the volume.
.
.It ATTR_VOL_MAXOBJCOUNT
A 
.Vt unsigned long 
containing the maximum number of file system objects that can be stored on the volume.
.
.It ATTR_VOL_MOUNTPOINT
An 
.Vt attrreference
structure containing the path to the volume's mount point as a 
UTF-8 encoded, null terminated C string.
The attribute data length will not be greater than 
.Dv MAXPATHLEN .
Equivalent to the 
.Fa f_mntonname 
field of the 
.Vt statfs 
structure returned by 
.Xr statfs 2 .
.
.It ATTR_VOL_NAME
(read/write) An 
.Vt attrreference
structure containing the name of the volume as a 
UTF-8 encoded, null terminated C string.
The attribute data length will not be greater than 
.Dv NAME_MAX +
1.
.Pp
.
This attribute is only read/write if the 
.Dv VOL_CAP_INT_VOL_RENAME
bit is set in the volume capabilities (see below).
.Pp
.
.It ATTR_VOL_MOUNTFLAGS
A 
.Vt unsigned long 
containing the volume mount flags. 
This is a copy of the value passed to the 
.Fa flags
parameter of 
.Xr mount 2
when the volume was mounted.
Equivalent to the 
.Fa f_flags 
field of the 
.Vt statfs 
structure returned by 
.Xr statfs 2 .
.
.It ATTR_VOL_MOUNTEDDEVICE
An 
.Vt attrreference
structure that returns the same value as the 
.Fa f_mntfromname 
field of the 
.Vt statfs 
structure returned by 
.Xr statfs 2 .
For local volumes this is the path to the device on which the volume is mounted as a 
UTF-8 encoded, null terminated C string.
For network volumes, this is a unique string that identifies the mount.
The attribute data length will not be greater than 
.Dv MAXPATHLEN .
.Pp
.
.It ATTR_VOL_ENCODINGSUSED
An 
.Vt unsigned long long
containing a bitmap of the text encodings used on this volume. 
For more information about this, see the discussion of 
.Fa encodingsBitmap 
in DTS Technote 1150 "HFS Plus Volume Format".
.
.It ATTR_VOL_CAPABILITIES
A
.Vt vol_capabilities_attr_t
structure describing the optional features supported by this volume. 
See below for a discussion of volume capabilities.
.
.It ATTR_VOL_ATTRIBUTES
A
.Vt vol_attributes_attr_t
structure describing the attributes supported by this volume. 
This structure is discussed below, along with volume capabilities.
.
.El
.
.Sh DIRECTORY ATTRIBUTES
.
The following directory attributes are defined.
.
.Bl -tag -width ATTR_VOL_ALLOCATIONCLUMP
.
.It ATTR_DIR_LINKCOUNT
A 
.Vt unsigned long 
containing the number of file system objects in the directory, including 
synthetic items such as "." and "..". 
For historical reasons, you should not always rely on this value being accurate.
.Pp
If you're implementing a volume format on which this is hard to calculate, 
you should not support this attribute. 
While it's traditional to return a constant value of 1 in the 
.Fa st_nlink 
field of the 
.Vt stat
structure as returned by 
.Xr stat 2 ,
it's not necessary to do this here because there is a 
defined way to indicate that you do not support the attribute.
.
.It ATTR_DIR_ENTRYCOUNT
A 
.Vt unsigned long 
containing the number of file system objects in the directory, not including 
any synthetic items.
.
.It ATTR_DIR_MOUNTSTATUS
A 
.Vt unsigned long 
containing flags describing what's mounted on the directory. 
Currently the only flag defined is 
.Dv DIR_MNTSTATUS_MNTPOINT, 
which indicates that there is a file system mounted on this directory.
Due to a bug (r. 3502822), this flag is never set on current system.
.
.El
.
.Sh FILE ATTRIBUTES
.
The following file attributes are defined.
.
.Bl -tag -width ATTR_VOL_ALLOCATIONCLUMP
.
.It ATTR_FILE_LINKCOUNT
A 
.Vt unsigned long
containing the number of hard links to this file. 
Equivalent to the 
.Fa st_nlink 
field of the 
.Vt stat 
structure returned by 
.Xr stat 2 .
.
.It ATTR_FILE_TOTALSIZE
An 
.Vt off_t
containing the total number of bytes in all forks of the file (the logical size).
.
.It ATTR_FILE_ALLOCSIZE
An 
.Vt off_t
containing a count of the bytes on disk used by all of the file's forks (the physical size).
.
.It ATTR_FILE_IOBLOCKSIZE
A 
.Vt unsigned long
containing the optimal block size when reading or writing this file's data. 
.
.It ATTR_FILE_CLUMPSIZE
A 
.Vt unsigned long
containing the allocation clump size for this file, in bytes. 
As the file is extended, the file system will attempt to allocate 
this much space each time in order to reduce fragmentation. 
This value applies to the data fork.
.
.It ATTR_FILE_DEVTYPE
(read/write) A 
.Vt unsigned long
containing the device type for a special device file. 
Equivalent to the 
.Fa st_rdev 
field of the 
.Vt stat 
structure returned by 
.Xr stat 2 .
.
.It ATTR_FILE_FILETYPE
A
.Vt unsigned long
that whose value is reserved.
Clients should ignore its value.
New volume format implementations should not support this attribute.
.
.It ATTR_FILE_FORKCOUNT
A
.Vt unsigned long
containing the number of forks in the file.
No built-in file systems on Mac OS X currently support forks other 
than the data and resource fork.
.
.It ATTR_FILE_FORKLIST
An 
.Vt attrreference
structure containing a list of named forks of the file.
No built-in file systems on Mac OS X currently support forks 
other than the data and resource fork.
Because of this, the structure of this attribute's value is not yet defined.
.
.It ATTR_FILE_DATALENGTH
An
.Vt off_t
containing the length of the data fork in bytes (the logical size).
.
.It ATTR_FILE_DATAALLOCSIZE
An
.Vt off_t
containing a count of the bytes on disk used by the data fork (the physical size).
.
.It ATTR_FILE_DATAEXTENTS
An
.Vt extentrecord
array for the data fork. 
The array contains eight 
.Vt diskextent 
structures which represent the first 
eight extents of the fork.
.Pp
This attributes exists for compatibility reasons. 
New clients should not use this attribute.
Rather, they should use the 
.Dv F_LOG2PHYS 
command in 
.Xr fcntl 2 .
.Pp
.
In current implementations the value may not be entirely accurate for 
a variety of reasons.
.
.It ATTR_FILE_RSRCLENGTH
An
.Vt off_t
containing the length of the resource fork in bytes (the logical size).
.
.It ATTR_FILE_RSRCALLOCSIZE
An
.Vt off_t
containing a count of the bytes on disk used by the resource fork (the physical size).
.
.It ATTR_FILE_RSRCEXTENTS
An
.Vt extentrecord
array for the resource fork. 
The array contains eight 
.Vt diskextent 
structures which represent the first 
eight extents of the fork.
.Pp
See also 
.Dv ATTR_FILE_DATAEXTENTS .
.
.El
.
.Sh FORK ATTRIBUTES
.
Fork attributes relate to the actual data in the file, 
which can be held in multiple named contiguous ranges, or forks.
The following fork attributes are defined.
.
.Bl -tag -width ATTR_VOL_ALLOCATIONCLUMP
.
.It ATTR_FORK_TOTALSIZE
An
.Vt off_t
containing the length of the fork in bytes (the logical size).
.
.It ATTR_FORK_ALLOCSIZE
An
.Vt off_t
containing a count of the bytes on disk used by the fork (the physical size).
.
.El
.Pp
.
Fork attributes are not properly implemented by any current Mac OS X 
volume format implementation. 
We strongly recommend that client programs do not request fork attributes. 
If you are implementing a volume format, you should not support these attributes. 
.
.Sh VOLUME CAPABILITIES
.
.\" vol_capabilities_attr_t
.
Not all volumes support all features.  The 
.Dv ATTR_VOL_CAPABILITIES 
attribute returns a 
.Vt vol_capabilities_attr_t 
structure (shown below) that indicates which features are supported by the volume.
.
.Bd -literal
typedef u_int32_t vol_capabilities_set_t[4];
.Pp
.
#define VOL_CAPABILITIES_FORMAT     0
#define VOL_CAPABILITIES_INTERFACES 1
#define VOL_CAPABILITIES_RESERVED1  2
#define VOL_CAPABILITIES_RESERVED2  3
.Pp
.
typedef struct vol_capabilities_attr {
    vol_capabilities_set_t capabilities;
    vol_capabilities_set_t valid;
} vol_capabilities_attr_t;
.Ed
.Pp
.
The structure contains two fields, 
.Fa capabilities 
and 
.Fa valid .
Each consists of an array of four elements. 
The arrays are indexed by the following values.
.
.Bl -tag -width VOL_CAP_FMT_PERSISTENTOBJECTIDS
.
.It VOL_CAPABILITIES_FORMAT
This element contains information about the volume format. 
See 
.Dv VOL_CAP_FMT_PERSISTENTOBJECTIDS 
and so on, below.
.
.It VOL_CAPABILITIES_INTERFACES
This element contains information about which optional functions are 
supported by the volume format implementation.
See 
.Dv VOL_CAP_INT_SEARCHFS 
and so on, below.
.
.It VOL_CAPABILITIES_RESERVED1
Reserved. 
A file system implementation should set this element to zero. 
A client program should ignore this element.
.
.It VOL_CAPABILITIES_RESERVED2
Reserved. 
A file system implementation should set this element to zero. 
A client program should ignore this element.
.
.El
.Pp
.
The 
.Fa valid 
field contains bit sets that indicate which flags are known to the volume format 
implementation. 
Each bit indicates whether the contents of the corresponding bit in the 
.Fa capabilities 
field is valid.
.Pp
.
The 
.Fa capabilities 
field contains bit sets that indicate whether a particular feature is implemented 
by this volume format. 
.Pp
.
The following bits are defined in the first element (indexed by 
.Dv VOL_CAPABILITIES_FORMAT ) 
of the 
.Fa capabilities 
and 
.Fa valid 
fields of the 
.Vt vol_capabilities_attr_t 
structure.
.
.Bl -tag -width VOL_CAP_FMT_PERSISTENTOBJECTIDS
.
.It VOL_CAP_FMT_PERSISTENTOBJECTIDS
If this bit is set the volume format supports persistent object identifiers 
and can look up file system objects by their IDs.
See 
.Dv ATTR_CMN_OBJPERMANENTID 
for details about how to obtain these identifiers.
.
.It VOL_CAP_FMT_SYMBOLICLINKS
If this bit is set the volume format supports symbolic links. 
.
.It VOL_CAP_FMT_HARDLINKS
If this bit is set the volume format supports hard links. 
.
.It VOL_CAP_FMT_JOURNAL
If this bit is set the volume format supports a journal used to 
speed recovery in case of unplanned restart (such as a power outage 
or crash).
This does not necessarily mean the volume is actively using a journal.
.Pp
Introduced with Darwin 7.0 (Mac OS X version 10.3).
.
.It VOL_CAP_FMT_JOURNAL_ACTIVE
If this bit is set the volume is currently using a journal for 
speedy recovery after an unplanned restart.
This bit can be set only if 
.Dv VOL_CAP_FMT_JOURNAL
is also set.
.Pp
Introduced with Darwin 7.0 (Mac OS X version 10.3).
.
.It VOL_CAP_FMT_NO_ROOT_TIMES
If this bit is set the volume format does not store reliable times for 
the root directory, so you should not depend on them to detect changes, 
identify volumes across unmount/mount, and so on.
.Pp
Introduced with Darwin 7.0 (Mac OS X version 10.3).
.
.It VOL_CAP_FMT_SPARSE_FILES
If this bit is set the volume format supports sparse files,
that is, files which can have 'holes' that have never been written
to, and thus do not consume space on disk. 
A sparse file may have an allocated size on disk that is less than its logical length (that is,
.Dv ATTR_FILE_ALLOCSIZE 
<
.Dv ATTR_FILE_TOTALSIZE ).
.
.Pp
Introduced with Darwin 7.0 (Mac OS X version 10.3).
.
.It VOL_CAP_FMT_ZERO_RUNS
For security reasons, parts of a file (runs) that have never been 
written to must appear to contain zeroes. 
When this bit is set, the volume keeps track of allocated but unwritten
runs of a file so that it can substitute zeroes without actually
writing zeroes to the media. 
This provides performance similar to sparse files, but not the space savings.
.Pp
Introduced with Darwin 7.0 (Mac OS X version 10.3).
.
.It VOL_CAP_FMT_CASE_SENSITIVE
If this bit is set the volume format treats upper and lower case 
characters in file and directory names as different. 
Otherwise an upper case character is equivalent to a lower case character, 
and you can't have two names that differ solely in the case of
the characters.
.Pp
Introduced with Darwin 7.0 (Mac OS X version 10.3).
.
.It VOL_CAP_FMT_CASE_PRESERVING
If this bit is set the volume format preserves the case of 
file and directory names. 
Otherwise the volume may change the case of some characters 
(typically making them all upper or all lower case).
A volume that sets 
.Dv VOL_CAP_FMT_CASE_SENSITIVE
must also set 
.Dv VOL_CAP_FMT_CASE_PRESERVING .
.Pp
Introduced with Darwin 7.0 (Mac OS X version 10.3).
.
.It VOL_CAP_FMT_FAST_STATFS
This bit is used as a hint to upper layers (specifically the Carbon File Manager) to 
indicate that 
.Xr statfs 2
is fast enough that its results need not be cached by the caller. 
A volume format implementation that caches the 
.Xr statfs 2 
information in memory should set this bit.
An implementation that must always read from disk or always perform a network 
transaction to satisfy 
.Xr statfs 2
should not set this bit.
.Pp
Introduced with Darwin 7.0 (Mac OS X version 10.3).
.
.It VOL_CAP_FMT_2TB_FILESIZE
If this bit is set the volume format supports file 
sizes upto 2TB.  This bit does not necessarily mean that the file 
system does not support file size more than 2TB.   This bit does 
not mean that the currently available space on the volume is 2TB. 
.Pp
Introduced with Darwin 8.0 (Mac OS X version 10.4).
.
.El
.Pp
.
The following bits are defined in the second element (indexed by 
.Dv VOL_CAPABILITIES_INTERFACES ) 
of the 
.Fa capabilities 
and 
.Fa valid 
fields of the 
.Vt vol_capabilities_attr_t 
structure.
.
.Bl -tag -width VOL_CAP_FMT_PERSISTENTOBJECTIDS
.
.It VOL_CAP_INT_SEARCHFS
If this bit is set the volume format implementation supports 
.Xr searchfs 2 .
.
.It VOL_CAP_INT_ATTRLIST
If this bit is set the volume format implementation supports 
.Fn getattrlist 
and 
.Xr setattrlist 2 .
.
.It VOL_CAP_INT_NFSEXPORT
If this bit is set the volume format implementation allows this volume to be exported via NFS. 
.
.It VOL_CAP_INT_READDIRATTR
If this bit is set the volume format implementation supports 
.Xr getdirentriesattr 2 .
.
.It VOL_CAP_INT_EXCHANGEDATA
If this bit is set the volume format implementation supports 
.Xr exchangedata 2 .
.Pp
Introduced with Darwin 7.0 (Mac OS X version 10.3).
.
.It VOL_CAP_INT_COPYFILE
If this bit is set the volume format implementation supports the (private and undocumented)
copyfile() function.
.Pp
Introduced with Darwin 7.0 (Mac OS X version 10.3).
.
.It VOL_CAP_INT_ALLOCATE
If this bit is set the volume format implementation supports the 
.Dv F_PREALLOCATE 
selector of 
.Xr fcntl 2 .
.Pp
Introduced with Darwin 7.0 (Mac OS X version 10.3).
.
.It VOL_CAP_INT_VOL_RENAME
If this bit is set the volume format implementation allows you to 
modify the volume name using 
.Xr setattrlist 2 .
.Pp
Introduced with Darwin 7.0 (Mac OS X version 10.3).
.
.It VOL_CAP_INT_ADVLOCK
If this bit is set the volume format implementation supports 
advisory locking, that is, the 
.Dv F_GETLK ,
.Dv F_SETLK , 
and 
.Dv F_SETLKW 
selectors to 
.Xr fcntl 2 .
.Pp
Introduced with Darwin 7.0 (Mac OS X version 10.3).
.
.It VOL_CAP_INT_FLOCK
If this bit is set the volume format implementation supports 
whole file locks. 
This includes 
.Xr flock 2 
and the 
.Dv O_EXLOCK 
and 
.Dv O_SHLOCK 
flags to 
.Xr open 2 .
.Pp
Introduced with Darwin 7.0 (Mac OS X version 10.3).
.
.El
.Pp
.
.\" vol_attributes_attr_t
.
A volume can also report which attributes it supports. 
This information is returned by the
.Dv ATTR_VOL_ATTRIBUTES 
attribute, which returns a 
.Vt vol_attributes_attr_t 
structure (shown below).
.
.Bd -literal
typedef struct attribute_set {
    attrgroup_t commonattr; /* common attribute group */
    attrgroup_t volattr;    /* volume attribute group */
    attrgroup_t dirattr;    /* directory attribute group */
    attrgroup_t fileattr;   /* file attribute group */
    attrgroup_t forkattr;   /* fork attribute group */
} attribute_set_t;
.Pp
.
typedef struct vol_attributes_attr {
    attribute_set_t validattr;
    attribute_set_t nativeattr;
} vol_attributes_attr_t;
.Ed
.Pp
.
The 
.Fa validattr 
field consists of a number of bit sets that indicate whether an attribute is 
supported by the volume format implementation. 
The 
.Fa nativeattr 
is similar except that the bit sets indicate whether an attribute is supported 
natively by the volume format. 
An attribute is supported natively if the volume format implementation does not have to do 
any complex conversions to access the attribute. 
For example, a volume format might support persistent object identifiers, but 
doing so requires a complex table lookup that is not part of the core volume 
format. 
In that case, the 
.Dv ATTR_VOL_ATTRIBUTES 
attribute would return 
.Dv ATTR_CMN_OBJPERMANENTID 
set in the 
.Fa validattr 
field of the 
.Vt vol_attributes_attr_t ,
but not in the 
.Fa nativeattr 
field.
.
.Sh RETURN VALUES
Upon successful completion a value of 0 is returned.
Otherwise, a value of -1 is returned and
.Va errno
is set to indicate the error.
.
.Sh COMPATIBILITY
Not all volumes support 
.Fn getattrlist .
The best way to test whether a volume supports this function is to 
simply call it and check the error result.
.Fn getattrlist 
will return  
.Dv ENOTSUP
if it is not supported on a particular volume.
.Pp
.
The 
.Fn getattrlist 
function has been undocumented for more than two years. 
In that time a number of volume format implementations have been created without 
a proper specification for the behaviour of this routine. 
You may encounter volume format implementations with slightly different 
behaviour than what is described here. 
Your program is expected to be tolerant of this variant behaviour.
.Pp
.
If you're implementing a volume format that supports 
.Fn getattrlist ,
you should be careful to support the behaviour specified by this document.
.
.Sh ERRORS
.Fn getattrlist
will fail if:
.Bl -tag -width Er
.
.It Bq Er ENOTSUP
The volume does not support
.Fn getattrlist .
.
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.
.It Bq Er ENAMETOOLONG
A component of a path name exceeded 
.Dv NAME_MAX
characters, or an entire path name exceeded 
.Dv PATH_MAX
characters.
.
.It Bq Er ENOENT
The file system object does not exist.
.
.It Bq Er EACCES
Search permission is denied for a component of the path prefix.
.
.It Bq Er ELOOP
Too many symbolic links were encountered in translating the pathname.
.
.It Bq Er EFAULT
.Fa path ,
.Fa attrList
or
.Em attrBuf
points to an invalid address.
.
.It Bq Er EINVAL
The 
.Fa bitmapcount 
field of 
.Fa attrList 
is not 
.Dv ATTR_BIT_MAP_COUNT .
.
.It Bq Er EINVAL
You requested an invalid attribute.
.
.It Bq Er EINVAL
You requested an attribute that is not supported for this file system object.
.
.It Bq Er EINVAL
You requested volume attributes and directory or file attributes.
.
.It Bq Er EINVAL
You requested volume attributes but 
.Fa path 
does not reference the root of the volume.
.
.It Bq Er EROFS
The volume is read-only but must be modified in order to return this attribute.
.
.It Bq Er EIO
An I/O error occurred while reading from or writing to the file system.
.El
.Pp
.
.Sh CAVEATS
.
If you request any volume attributes, you must set 
.Dv ATTR_VOL_INFO 
in the 
.Fa volattr
field, even though it generates no result in the attribute buffer.
.Pp
.
The order that attributes are stored in the attribute buffer almost 
invariably matches the order of attribute mask bit values.
For example, 
.Dv ATTR_CMN_NAME 
(0x00000001) comes before 
.Dv ATTR_CMN_DEVID 
(0x00000002) because its value is smaller.
However, you can not rely on this ordering because there is one key exception:
.Dv ATTR_CMN_FLAGS 
is placed after the 
.Dv ATTR_CMN_NAMEDATTRCOUNT
/
.Dv ATTR_CMN_NAMEDATTRLIST 
pair, even though its bit position indicates that it should come before. 
This is due to a bug in an early version of Mac OS X that can't be fixed for 
binary compatibility reasons. 
When ordering attributes, you should always use the order in which they 
are described above.
.Pp
.
For more caveats, see also the compatibility notes above.
.
.Sh EXAMPLES
.
The following code prints the file type and creator of a file, 
assuming that the volume supports the required attributes.
.
.Bd -literal
#include <assert.h>
#include <stdio.h>
#include <string.h>
#include <sys/attr.h>
#include <sys/errno.h>
#include <unistd.h>
#include <sys/vnode.h>
.Pp
.
typedef struct attrlist attrlist_t;
.Pp
.
struct FInfoAttrBuf {
    unsigned long   length;
    fsobj_type_t    objType;
    char            finderInfo[32];
};
typedef struct FInfoAttrBuf FInfoAttrBuf;
.Pp
.
static int FInfoDemo(const char *path)
{
    int             err;
    attrlist_t      attrList;
    FInfoAttrBuf    attrBuf;
.Pp
.
    memset(&attrList, 0, sizeof(attrList));
    attrList.bitmapcount = ATTR_BIT_MAP_COUNT;
    attrList.commonattr  = ATTR_CMN_OBJTYPE | ATTR_CMN_FNDRINFO;
.Pp
    
    err = getattrlist(path, &attrList, &attrBuf, sizeof(attrBuf), 0);
    if (err != 0) {
        err = errno;
    }
.Pp
    
    if (err == 0) {
        assert(attrBuf.length == sizeof(attrBuf));
.Pp
        
        printf("Finder information for %s:\en", path);
        switch (attrBuf.objType) {
            case VREG:
                printf("file type    = '%.4s'\en", &attrBuf.finderInfo[0]);
                printf("file creator = '%.4s'\en", &attrBuf.finderInfo[4]);
                break;
            case VDIR:
                printf("directory\en");
                break;
            default:
                printf("other object type, %d\en", attrBuf.objType);
                break;
        }
    }
.Pp
.
    return err;
}
.Ed
.Pp
.
The following code is an alternative implementation that uses nested structures 
to group the related attributes.
.
.Bd -literal
#include <assert.h>
#include <stdio.h>
#include <stddef.h>
#include <string.h>
#include <sys/attr.h>
#include <sys/errno.h>
#include <unistd.h>
#include <sys/vnode.h>
.Pp
.
typedef struct attrlist attrlist_t;
.Pp
.
struct FInfo2CommonAttrBuf {
    fsobj_type_t    objType;
    char            finderInfo[32];
};
typedef struct FInfo2CommonAttrBuf FInfo2CommonAttrBuf;
.Pp
.
struct FInfo2AttrBuf {
    unsigned long       length;
    FInfo2CommonAttrBuf common;
};
typedef struct FInfo2AttrBuf FInfo2AttrBuf;
.Pp
.
static int FInfo2Demo(const char *path)
{
    int             err;
    attrlist_t      attrList;
    FInfo2AttrBuf   attrBuf;
.Pp
.
    memset(&attrList, 0, sizeof(attrList));
    attrList.bitmapcount = ATTR_BIT_MAP_COUNT;
    attrList.commonattr  = ATTR_CMN_OBJTYPE | ATTR_CMN_FNDRINFO;
.Pp
.
    err = getattrlist(path, &attrList, &attrBuf, sizeof(attrBuf), 0);
    if (err != 0) {
        err = errno;
    }
.Pp
.
    if (err == 0) {
        assert(attrBuf.length == sizeof(attrBuf));
.Pp
.
        printf("Finder information for %s:\en", path);
        switch (attrBuf.common.objType) {
            case VREG:
                printf(
                    "file type    = '%.4s'\en", 
                    &attrBuf.common.finderInfo[0]
                );
                printf(
                    "file creator = '%.4s'\en", 
                    &attrBuf.common.finderInfo[4]
                );
                break;
            case VDIR:
                printf("directory\en");
                break;
            default:
                printf(
                    "other object type, %d\en", 
                    attrBuf.common.objType
                );
                break;
        }
    }
.Pp
.
    return err;
}
.Ed
.Pp
.
The following example shows how to deal with variable length attributes. 
It assumes that the volume specified by 
.Fa path 
supports the necessary attributes.
.
.Bd -literal
#include <assert.h>
#include <stdio.h>
#include <stddef.h>
#include <string.h>
#include <sys/attr.h>
#include <sys/errno.h>
#include <unistd.h>
#include <sys/vnode.h>
.Pp
.
typedef struct attrlist attrlist_t;
.Pp
.
struct VolAttrBuf {
    unsigned long   length;
    unsigned long   fileCount;
    unsigned long   dirCount;
    attrreference_t mountPointRef;
    attrreference_t volNameRef;
    char            mountPointSpace[MAXPATHLEN];
    char            volNameSpace[MAXPATHLEN];
};
typedef struct VolAttrBuf VolAttrBuf;
.Pp
.
static int VolDemo(const char *path)
{
    int             err;
    attrlist_t      attrList;
    VolAttrBuf      attrBuf;
.Pp
.
    memset(&attrList, 0, sizeof(attrList));
    attrList.bitmapcount = ATTR_BIT_MAP_COUNT;
    attrList.volattr     =   ATTR_VOL_INFO 
                           | ATTR_VOL_FILECOUNT 
                           | ATTR_VOL_DIRCOUNT 
                           | ATTR_VOL_MOUNTPOINT 
                           | ATTR_VOL_NAME;
.Pp
    
    err = getattrlist(path, &attrList, &attrBuf, sizeof(attrBuf), 0);
    if (err != 0) {
        err = errno;
    }
.Pp
    
    if (err == 0) {
        assert(attrBuf.length >  offsetof(VolAttrBuf, mountPointSpace));
        assert(attrBuf.length <= sizeof(attrBuf));
.Pp
        
        printf("Volume information for %s:\en", path);
        printf("ATTR_VOL_FILECOUNT:  %lu\en", attrBuf.fileCount);
        printf("ATTR_VOL_DIRCOUNT:   %lu\en", attrBuf.dirCount);
        printf(
            "ATTR_VOL_MOUNTPOINT: %.*s\en", 
            (int) attrBuf.mountPointRef.attr_length,
            ( ((char *) &attrBuf.mountPointRef) 
              + attrBuf.mountPointRef.attr_dataoffset )
        );
        printf(
            "ATTR_VOL_NAME:       %.*s\en", 
            (int) attrBuf.volNameRef.attr_length,
            ( ((char *) &attrBuf.volNameRef) 
              + attrBuf.volNameRef.attr_dataoffset )
        );
    }
.Pp
.
    return err;
}
.Ed
.Pp
.
.Sh SEE ALSO
.
.Xr access 2 ,
.Xr chflags 2 ,
.Xr exchangedata 2 ,
.Xr fcntl 2 ,
.Xr getdirentriesattr 2 ,
.Xr mount 2 ,
.Xr searchfs 2 ,
.Xr setattrlist 2 ,
.Xr stat 2 ,
.Xr statfs 2
.
.Sh HISTORY
A 
.Fn getattrlist
function call appeared in Darwin 1.3.1 (Mac OS X version 10.0).
.