xnu-4570.41.2.tar.gz

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

diff --git a/bsd/man/man2/fcntl.2 b/bsd/man/man2/fcntl.2
index b53a38be18362ae4b64ff1f4972faad6ee107b34..b55972bd918aa12974e544e58f703fe6661998bf 100644 (file)
--- a/bsd/man/man2/fcntl.2
+++ b/bsd/man/man2/fcntl.2
@@ -71,7 +71,7 @@
 .Fa "..."
 .Fc
 .Sh DESCRIPTION
-.Fn Fcntl
+.Fn fcntl
 provides for control over descriptors.
 The argument
 .Fa fildes
@@ -155,6 +155,12 @@ or greater.
 Preallocate file storage space. Note: upon success, 
 the space that is allocated can be the same size or 
 larger than the space requested.
+.It Dv F_PUNCHHOLE
+Deallocate a region and replace it with a hole. Subsequent reads of the
+affected region will return bytes of zeros that are usually not backed by
+physical blocks. This will not change the actual file size. Holes must be
+aligned to file system block boundaries. This will fail on
+file systems that do not support this interface.
 .It Dv F_SETSIZE
 Truncate a file without zeroing space.
 The calling process must have root privileges.
@@ -182,9 +188,12 @@ A value of zero in
 turns data caching on.
 .It Dv F_LOG2PHYS
 Get disk device information.
-Currently this only includes the
+Currently this only returns the
 disk device address that corresponds
-to the current file offset.
+to the current file offset. Note that the system 
+may return -1 as the disk device address if the file is not 
+backed by physical blocks. This is subject
+to change.
 .It Dv F_LOG2PHYS_EXT
 Variant of F_LOG2PHYS that uses the passed in
 file offset and length.
@@ -488,6 +497,19 @@ Allocate from the volume offset.
 .El
 .Pp
 The
+.Dv F_PUNCHHOLE
+command operates on the following structure:
+.ne 7v
+.Bd -literal
+        typedef struct fpunchhole {
+            u_int32_t fp_flags;     /* unused */
+            u_int32_t reserved;     /* (to maintain 8-byte alignment) */
+            off_t     fp_offset;    /* IN: start of the region */
+            off_t     fp_length;    /* IN: size of the region */
+        } fpunchhole_t;
+.Ed
+.Pp
+The
 .Dv F_RDADVISE
 command operates on the following structure
 which holds information passed from the
@@ -708,6 +730,21 @@ is a negative or zero value.
 .Pp
 The argument
 .Fa cmd
+is
+.Dv F_PUNCHHOLE
+and
+either
+.Fa fp_offset
+or
+.Fa fp_length
+are negative, or both
+.Fa fp_offset
+and
+.Fa fp_length
+are not multiples of the file system block size.
+.Pp
+The argument
+.Fa cmd
 is either
 .Dv F_READBOOTSTRAP
 or