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into ffs_sbsearch() to allow use by other parts of the system. Historically only fsck_ffs(8), the UFS filesystem checker, had code to track down and use alternate UFS superblocks. Since fsdb(8) used much of the fsck_ffs(8) implementation it had some ability to track down alternate superblocks. This change extracts the code to track down alternate superblocks from fsck_ffs(8) and puts it into a new function ffs_sbsearch() in sys/ufs/ffs/ffs_subr.c. Like ffs_sbget() and ffs_sbput() also found in ffs_subr.c, these functions can be used directly by the kernel subsystems. Additionally they are exported to the UFS library, libufs(8) so that they can be used by user-level programs. The new functions added to libufs(8) are sbfind(3) that is an alternative to sbread(3) and sbsearch(3) that is an alternative to sbget(3). See their manual pages for further details. The utilities that have been changed to search for superblocks are dumpfs(8), fsdb(8), ffsinfo(8), and fsck_ffs(8). Also, the prtblknos(8) tool found in tools/diag/prtblknos searches for superblocks. The UFS specific mount code uses the superblock search interface when mounting the root filesystem and when the administrator doing a mount(8) command specifies the force flag (-f). The standalone UFS boot code (found in stand/libsa/ufs.c) uses the superblock search code in the hope of being able to get the system up and running so that fsck_ffs(8) can be used to get the filesystem cleaned up. The following utilities have not been changed to search for superblocks: clri(8), tunefs(8), snapinfo(8), fstyp(8), quot(8), dump(8), fsirand(8), growfs(8), quotacheck(8), gjournal(8), and glabel(8). When these utilities fail, they do report the cause of the failure. The one exception is the tasting code used to try and figure what a given disk contains. The tasting code will remain silent so as not to put out a slew of messages as it trying to taste every new mass storage device that shows up. Reviewed by: kib Reviewed by: Warner Losh Tested by: Peter Holm Differential Revision: https://reviews.freebsd.org/D36053 Sponsored by: The FreeBSD Foundation
206 lines
4.5 KiB
Groff
206 lines
4.5 KiB
Groff
.\" Author: Juli Mallett <jmallett@FreeBSD.org>
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.\" Date: June 04, 2003
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.\" Description:
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.\" Manual page for libufs functions:
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.\" sbget(3)
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.\" sbsearch(3)
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.\" sbput(3)
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.\" sbread(3)
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.\" sbfind(3)
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.\" sbwrite(3)
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.\"
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.\" This file is in the public domain.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd August 8, 2022
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.Dt SBREAD 3
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.Os
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.Sh NAME
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.Nm sbget , sbsearch , sbput , sbread , sbfind , sbwrite
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.Nd read and write superblocks of a UFS file system
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.Sh LIBRARY
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.Lb libufs
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.Sh SYNOPSIS
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.In sys/param.h
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.In sys/mount.h
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.In ufs/ufs/ufsmount.h
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.In ufs/ufs/dinode.h
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.In ufs/ffs/fs.h
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.In libufs.h
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.Ft int
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.Fn sbget "int devfd" "struct fs **fsp" "off_t sblockloc" "int flags"
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.Ft int
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.Fn sbsearch "int devfd" "struct fs **fsp" "int flags"
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.Ft int
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.Fn sbput "int devfd" "struct fs *fs" "int numaltwrite"
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.Ft int
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.Fn sbread "struct uufsd *disk"
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.Ft int
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.Fn sbfind "struct uufsd *disk" "int flags"
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.Ft int
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.Fn sbwrite "struct uufsd *disk" "int all"
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.Sh DESCRIPTION
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The
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.Fn sbget ,
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.Fn sbsearch ,
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.Fn sbread ,
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and
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.Fn sbfind
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functions provide superblock reads for
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.Xr libufs 3
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consumers.
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The
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.Fn sbput
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and
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.Fn sbwrite
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functions provide superblock writes for
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.Xr libufs 3
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consumers.
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.Pp
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The
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.Fn sbget
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and
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.Fn sbsearch
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functions first allocate a buffer to hold the superblock.
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Using the
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.Va devfd
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file descriptor that references the filesystem disk,
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.Fn sbget
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reads the superblock located at the byte offset specified by
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.Va sblockloc
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into the allocated buffer.
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The value
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.Cm UFS_STDSB
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may be specified for
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.Va sblockloc
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to request that the standard location for the superblock be read.
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The
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.Fn sbsearch
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function uses the
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.Va devfd
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file descriptor that references the filesystem disk,
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to search first for the superblock at the standard location.
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If it is not found or is too damaged to use
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.Fn sbsearch
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will attempt to find one of the filesystem's alternate superblocks.
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Flags are specified by
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.Em or Ns 'ing
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the following values:
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.Pp
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.Bl -tag -width UFS_NOCSUM
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.It Cm UFS_NOCSUM
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Causes only the superblock itself to be returned, but does not read in any
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auxiliary data structures like the cylinder group summary information.
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.It Cm UFS_NOMSG
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Indicates that superblock inconsistency error messages should not be printed.
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.El
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.Pp
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If successful,
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.Fn sbget
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and
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.Fn sbsearch
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functions return a pointer to the buffer containing the superblock in
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.Va fsp .
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The
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.Fn sbget
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and
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.Fn sbsearch
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functions are safe to use in threaded applications.
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.Pp
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The
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.Fn sbput
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function writes the superblock specified by
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.Va fs
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to the location from which it was read on the disk referenced by the
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.Va devfd
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file descriptor.
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Additionally, the
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.Fn sbput
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function will update the first
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.Va numaltwrite
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alternate superblock locations.
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To update all the alternate superblocks,
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specify a
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.Va numaltwrite
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value of
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.Va fs->fs_ncg .
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The
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.Fn sbput
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function is safe to use in threaded applications.
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Note that the
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.Fn sbput
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function needs to be called only if the superblock has been
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modified and the on-disk copy needs to be updated.
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.Pp
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The
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.Fn sbread
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function reads the standard filesystem superblock.
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The
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.Fn sbfind
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function tries to find a usable superblock.
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It searchs first for the superblock at the standard location.
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If it is not found or is too damaged to use
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.Fn sbfind
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will attempt to find one of the filesystem's alternate superblocks.
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If successful
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.Fn sbread
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and
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.Fn sbfind
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return a superblock in the
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.Va d_sb ,
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structure embedded in the given user-land UFS disk structure.
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.Pp
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The
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.Fn sbwrite
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function writes the superblock from the
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.Va d_sb ,
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structure embedded in the given user-land UFS disk structure
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to the location from which it was read.
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Additionally, the
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.Fn sbwrite
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function will write to all the alternate superblock locations if the
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.Fa all
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value is non-zero.
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.Sh RETURN VALUES
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.Rv -std sbread sbwrite
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The
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.Fn sbget ,
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.Fn sbsearch ,
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and
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.Fn sbput
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functions return the value 0 if successful;
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otherwise they return one of the errors described below.
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.Sh ERRORS
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The errors returned by
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.Fn sbget ,
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.Fn sbsearch ,
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.Fn sbread ,
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and
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.Fn sbfind ,
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include any of the errors specified for the library function
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.Xr bread 3 .
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Additionally, they may follow the
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.Xr libufs 3
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error methodologies in situations where no usable superblock could be
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found.
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.Pp
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The errors returned by
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.Fn sbput
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and
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.Fn sbwrite
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include any of the errors specified for the library function
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.Xr bwrite 3 .
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.Sh SEE ALSO
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.Xr bread 3 ,
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.Xr bwrite 3 ,
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.Xr libufs 3
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.Sh HISTORY
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These functions first appeared as part of
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.Xr libufs 3
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in
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.Fx 5.0 .
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.Sh AUTHORS
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.An Juli Mallett Aq Mt jmallett@FreeBSD.org
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.An Marshall Kirk McKusick Aq Mt mckusick@FreeBSD.org
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