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

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.\" under the License.
.\" 
.\"     @(#)getdirentriesattr.2
.
.Dd December 15, 2003
.Dt GETDIRENTRIESATTR 2
.Os Darwin
.Sh NAME
.Nm getdirentriesattr
.Nd get file system attributes for multiple directory entries
.Sh SYNOPSIS
.Fd #include <sys/attr.h>
.Fd #include <unistd.h>
.Ft int
.Fn getdirentriesattr "int fd" "struct attrlist * attrList" "void * attrBuf" "size_t attrBufSize" "unsigned long * count" "unsigned long * basep" "unsigned long * newState" "unsigned long options"
.
.
.Sh DESCRIPTION
The
.Fn getdirentriesattr
function reads directory entries and returns their attributes (that is, metadata). 
You can think of it as a combination of 
.Xr getdirentries 2
and
.Xr getattrlist 2 .
The function reads directory entries from the directory referenced by the 
file descriptor 
.Fa fd .
Attributes of those directory entries are placed into the buffer specified by 
.Fa attrBuf
and
.Fa attrBufSize .
The 
.Fa attrList 
parameter determines what attributes are returned for each entry.
The 
.Fa count 
parameter contains the number of directory entries requested and returned.
The 
.Fa basep
parameter returns the directory offset in a manner similar to 
.Xr getdirentries 2 .
The 
.Fa newState
parameter allows you to check whether the directory has been modified while 
you were reading it.
The 
.Fa options 
parameter lets you control specific aspects of the function's behaviour.
.Pp
.
The 
.Fn getdirentriesattr 
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 getdirentriesattr .
.Pp
.
.\" fd parameter
.
The
.Fa fd
parameter must be a file descriptor that references a directory that you have opened for reading. 
.Pp
.
.\" attrList parameter
.
The
.Fa attrList
parameter is a pointer to an 
.Vt attrlist 
structure. 
You are responsible for filling out all fields of this structure before calling the function. 
See the discussion of the  
.Xr getattrlist 2 
function for a detailed description of this structure. 
To get an attribute you must set the corresponding bit in the appropriate 
.Vt attrgroup_t 
field of the 
.Vt attrlist 
structure. 
You must not request volume attributes.
.Pp
.
.\" attrBuf and attrBufSize parameters
.
The
.Fa attrBuf
and 
.Fa attrBufSize
parameters specify a buffer into which the function places attribute values. 
The attributes for any given directory entry are grouped together and 
packed in exactly the same way as they are returned from 
.Xr getattrlist 2 .
These groups are then placed into the buffer, one after another. 
As each group starts with a leading 
.Vt unsigned long 
that contains the 
overall length of the group, you can step from one group to the next 
by simply adding this length to your pointer.
The sample code (below) shows how to do this.
The initial contents of this buffer are ignored.
.Pp
.
.\" count parameter
.
The 
.Fa count 
parameter points to a 
.Vt unsigned long 
variable. 
You should initialise this variable to be the number of directory entries for which 
you wish to get attributes.
On return, this variable contains the number of directory entries whose attributes 
have been placed into the attribute buffer.
This may be smaller than the number that you requested.
.Pp
.
.\" basep parameter
The 
.Fa basep 
parameter returns the offset of the last directory entry read, in a 
manner identical to 
.Xr getdirentries 2 . 
You can use this value to reset a directory iteration to a known position 
using 
.Xr lseek 2 .
The initial value of the variable is ignored.
.Pp
.
.\" newState parameter
.
The 
.Fa newState 
parameter returns a value that changes if the directory has been modified. 
If you're iterating through the directory by making repeated calls to 
.Fn getdirentriesattr ,
you can compare subsequent values of 
.Fa newState 
to determine whether the directory has been modified (and thus restart 
your iteration at the beginning).
The initial value of the variable is ignored.
.Pp
.
.\" options parameter
.
The
.Fa options
parameter is a bit set that controls the behaviour of
.Fn getdirentriesattr .
The following option bits are defined.
.
.Bl -tag -width FSOPT_NOINMEMUPDATE
.
.It FSOPT_NOINMEMUPDATE
This tells 
.Fn getdirentriesattr
to return the directory entries from disk rather than taking the extra step of looking 
at data structures in-memory which may contain changes that haven't been flushed to disk.
.Pp
This option allowed for specific performance optimizations for specific clients on older systems. 
We currently recommend that clients not set this option and that file system 
implementations ignore it.
.
.El
.Pp
It is typical to ask for a combination of common, file, and directory 
attributes and then use the value of the 
.Dv ATTR_CMN_OBJTYPE 
attribute to parse the resulting attribute buffer.
.
.Sh RETURN VALUES
Upon successful completion a value of 0 or 1 is returned. 
The value 0 indicates that the routine completed successfully. 
The value 1 indicates that the routine completed successfully and has 
returned the last entry in the directory.
On error, a value of -1 is returned and
.Va errno
is set to indicate the error.
.
.Sh COMPATIBILITY
Not all volumes support 
.Fn getdirentriesattr .
You can test whether a volume supports 
.Fn getdirentriesattr 
by using 
.Xr getattrlist 2 
to get the volume capabilities attribute 
.Dv ATTR_VOL_CAPABILITIES ,
and then testing the 
.Dv VOL_CAP_INT_READDIRATTR 
flag.
.Pp
.
The 
.Fn getdirentriesattr 
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 getdirentriesattr ,
you should be careful to support the behaviour specified by this document.
.
.Sh ERRORS
.Fn getdirentriesattr
will fail if:
.Bl -tag -width Er
.
.It Bq Er ENOTSUP
The volume does not support
.Fn getdirentriesattr .
.
.It Bq Er EBADF
.Fa fd 
is not a valid file descriptor for a directory open for reading.
.
.It Bq Er EFAULT
.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 volume attributes.
.
.It Bq Er EINVAL
The 
.Fa options 
parameter contains an invalid flag.
.
.It Bq Er EIO
An I/O error occurred while reading from or writing to the file system.
.El
.Pp
.
.Sh EXAMPLES
.
The following code lists the contents of a directory using 
.Fn getdirentriesattr . 
The listing includes the file type and creator for files.
.
.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>
#include <stdbool.h>
#include <fcntl.h>
.Pp
.
typedef struct attrlist attrlist_t;
.Pp
.
struct FInfoAttrBuf {
    unsigned long   length;
    attrreference_t name;
    fsobj_type_t    objType;
    char            finderInfo[32];
};
typedef struct FInfoAttrBuf FInfoAttrBuf;
.Pp
.
enum {
    kEntriesPerCall = 10
};
.Pp
.
static int FInfoDemo(const char *dirPath)
{
    int             err;
    int             junk;
    int             dirFD;
    attrlist_t      attrList;
    unsigned long   index;
    unsigned long   count;
    unsigned long   junkBaseP;
    bool            oldStateValid;
    unsigned long   oldState;
    unsigned long   newState;
    bool            done;
    FInfoAttrBuf *  thisEntry;
    char            attrBuf[kEntriesPerCall * (sizeof(FInfoAttrBuf) + 64)];
.Pp
.
    // attrBuf is big enough for kEntriesPerCall entries, assuming that 
    // the average name length is less than 64.
.Pp
.
    memset(&attrList, 0, sizeof(attrList));
    attrList.bitmapcount = ATTR_BIT_MAP_COUNT;
    attrList.commonattr  =    ATTR_CMN_NAME 
                            | ATTR_CMN_OBJTYPE 
                            | ATTR_CMN_FNDRINFO;
.Pp
    
    err = 0;
    dirFD = open(dirPath, O_RDONLY, 0);
    if (dirFD < 0) {
        err = errno;
    }
    if (err == 0) {
        oldStateValid = false;
        done = false;
        do {
            count = kEntriesPerCall;
.Pp
            err = getdirentriesattr(
                dirFD, 
                &attrList, 
                &attrBuf, 
                sizeof(attrBuf), 
                &count, 
                &junkBaseP, 
                &newState, 
                0
            );
            if (err < 0) {
                err = errno;
            } else {
                done = err;
                err = 0;
            }
.Pp
            if (err == 0) {
                if (oldStateValid) {
                    if (newState != oldState) {
                        printf("*** Directory has changed\en");
                        oldState = newState;
                    }
                } else {
                    oldState = newState;
                    oldStateValid = true;
                }
.Pp
                thisEntry = (FInfoAttrBuf *) attrBuf;
.Pp
                for (index = 0; index < count; index++) {
                    switch (thisEntry->objType) {
                        case VREG:
                            printf(
                                "'%4.4s' '%4.4s' ", 
                                &thisEntry->finderInfo[0], 
                                &thisEntry->finderInfo[4]
                            );
                            break;
                        case VDIR:
                            printf("directory     ");
                            break;
                        default:
                            printf(
                                "objType = %-2d  ", 
                                thisEntry->objType
                            );
                            break;
                    }
                    printf(
                        "%s\en", 
                        ((char *) &thisEntry->name) 
                            + thisEntry->name.attr_dataoffset
                    );
.Pp
                    // Advance to the next entry.
.Pp
                    ((char *) thisEntry) += thisEntry->length;
                }
            }
        } while ( err == 0 && ! done );
    }
.Pp
    if (dirFD != -1) {
        junk = close(dirFD);
        assert(junk == 0);
    }
.Pp
    return err;
}
.Ed
.Pp
.
.Sh SEE ALSO
.
.Xr getattrlist 2 ,
.Xr getdirentries 2 ,
.Xr lseek 2
.
.Sh HISTORY
A
.Fn getdirentriesattr
function call appeared in Darwin 1.3.1 (Mac OS X version 10.0).
.