Implement SEEK_DATA and SEEK_HOLE extensions to lseek(2) as found in
OpenSolaris. For more information please refer to: http://blogs.sun.com/bonwick/entry/seek_hole_and_seek_data
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Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=168397
@ -200,6 +200,12 @@ __END_DECLS
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#ifndef SEEK_END
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#define SEEK_END 2 /* set file offset to EOF plus offset */
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#endif
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#ifndef SEEK_DATA
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#define SEEK_DATA 3 /* set file offset to next data past offset */
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#endif
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#ifndef SEEK_HOLE
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#define SEEK_HOLE 4 /* set file offset to next hole past offset */
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#endif
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#define stdin __stdinp
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#define stdout __stdoutp
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@ -87,6 +87,23 @@ the offset is set to the size of the
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file plus
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.Fa offset
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bytes.
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.It
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If
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.Fa whence
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is
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.Dv SEEK_HOLE ,
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the offset of the start of the next hole greater than or equal to the supplied
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.Fa offset
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is returned.
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The definition of a hole is provided below.
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.It
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If
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.Fa whence
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is
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.Dv SEEK_DATA ,
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the offset is set to the start of the next non-hole file region greater
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than or equal to the supplied
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.Fa offset .
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.El
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.Pp
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The
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@ -100,6 +117,33 @@ bytes of zeros (until data is actually written into the gap).
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Some devices are incapable of seeking.
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The value of the pointer
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associated with such a device is undefined.
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.Pp
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A
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.Qq hole
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is defined as a contiguous range of bytes in a file, all having the value of
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zero, but not all zeros in a file are guaranteed to be represented as holes
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returned with
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.Dv SEEK_HOLE .
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File systems are allowed to expose ranges of zeros with
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.Dv SEEK_HOLE ,
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but not required to.
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Applications can use
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.Dv SEEK_HOLE
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to optimise their behavior for ranges of zeros, but must not depend on it to
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find all such ranges in a file.
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The existence of a hole at the end of every data region allows for easy
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programming and implies that a virtual hole exists at the end of the file.
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Applications should use
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.Fn fpathconf _PC_MIN_HOLE_SIZE
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or
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.Fn pathconf _PC_MIN_HOLE_SIZE
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to determine if a file system supports
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.Dv SEEK_HOLE .
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See
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.Xr pathconf 2 .
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.Pp
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For file systems that do not supply information about holes, the file will be
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represented as one entire data region.
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.Sh RETURN VALUES
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Upon successful completion,
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.Fn lseek
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@ -128,6 +172,13 @@ argument
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is not a proper value
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or the resulting file offset would
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be negative for a non-character special file.
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.It Bq Er ENXIO
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For
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.Dv SEEK_DATA ,
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there are no more data regions past the supplied offset.
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For
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.Dv SEEK_HOLE ,
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there are no more holes past the supplied offset.
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.It Bq Er EOVERFLOW
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The resulting file offset would be a value which cannot be represented
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correctly in an object of type
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@ -140,7 +191,8 @@ is associated with a pipe, socket, or FIFO.
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.El
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.Sh SEE ALSO
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.Xr dup 2 ,
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.Xr open 2
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.Xr open 2 ,
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.Xr pathconf 2
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.Sh STANDARDS
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The
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.Fn lseek
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@ -144,6 +144,17 @@ otherwise 0.
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.It Li _PC_MAC_PRESENT
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Returns 1 if a Mandatory Access Control (MAC) label can be set on the
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specified file, otherwise 0.
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.It Li _PC_MIN_HOLE_SIZE
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If a file system supports the reporting of holes (see
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.Xr lseek 2 ,
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.Fn pathconf
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and
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.Fn fpathconf
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return a positive number that represents the minimum hole size returned in
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bytes.
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The offsets of holes returned will be aligned to this same value.
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A special value of 1 is returned if the file system does not specify the minimum
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hole size but still reports holes.
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.El
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.Sh RETURN VALUES
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If the call to
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@ -216,6 +227,7 @@ is not a valid open file descriptor.
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An I/O error occurred while reading from or writing to the file system.
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.El
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.Sh SEE ALSO
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.Xr lseek 2 ,
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.Xr sysctl 3
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.Sh HISTORY
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The
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@ -54,6 +54,7 @@ __FBSDID("$FreeBSD$");
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#include <sys/kernel.h>
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#include <sys/fcntl.h>
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#include <sys/file.h>
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#include <sys/filio.h>
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#include <sys/limits.h>
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#include <sys/linker.h>
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#include <sys/stat.h>
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@ -1740,6 +1741,12 @@ lseek(td, uap)
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break;
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case L_SET:
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break;
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case SEEK_DATA:
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error = fo_ioctl(fp, FIOSEEKDATA, &offset, cred, td);
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break;
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case SEEK_HOLE:
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error = fo_ioctl(fp, FIOSEEKHOLE, &offset, cred, td);
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break;
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default:
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error = EINVAL;
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}
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@ -55,5 +55,8 @@ struct fiodgname_arg {
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void *buf;
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};
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#define FIODGNAME _IOW('f', 120, struct fiodgname_arg) /* get dev. name */
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/* Handle lseek SEEK_DATA and SEEK_HOLE for holey file knowledge. */
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#define FIOSEEKDATA _IOWR('f', 97, off_t) /* SEEK_DATA */
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#define FIOSEEKHOLE _IOWR('f', 98, off_t) /* SEEK_HOLE */
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#endif /* !_SYS_FILIO_H_ */
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@ -107,6 +107,8 @@
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#define SEEK_SET 0 /* set file offset to offset */
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#define SEEK_CUR 1 /* set file offset to current plus offset */
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#define SEEK_END 2 /* set file offset to EOF plus offset */
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#define SEEK_DATA 3 /* set file offset to next data past offset */
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#define SEEK_HOLE 4 /* set file offset to next hole past offset */
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#endif
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#ifndef _POSIX_SOURCE
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@ -151,6 +153,9 @@
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#define _PC_MAC_PRESENT 63
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#endif
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/* From OpenSolaris, used by SEEK_DATA/SEEK_HOLE. */
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#define _PC_MIN_HOLE_SIZE 21
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#if __BSD_VISIBLE
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/*
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* rfork() options.
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