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204 lines
4.5 KiB
Groff
204 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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.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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