dffce2150e
Specifically reading is done if ffs_sbget() and writing is done in ffs_sbput(). These functions are exported to libufs via the sbget() and sbput() functions which then used in the various filesystem utilities. This work is in preparation for adding subperblock check hashes. No functional change intended. Reviewed by: kib
146 lines
3.0 KiB
Groff
146 lines
3.0 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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.\" sbput(3)
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.\" sbread(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 January 19, 2018
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.Dt SBREAD 3
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.Os
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.Sh NAME
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.Nm sbget , sbput , sbread , 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"
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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 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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and
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.Fn sbread
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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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function first allocates 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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If successful, it returns 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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function is 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 into 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 sbget sbput sbread sbwrite
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.Sh ERRORS
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The
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.Fn sbget
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and
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.Fn sbread
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functions may fail and set
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.Va errno
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for any of the errors specified for the library function
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.Xr bread 3 .
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Additionally, it 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
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.Fn sbput
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and
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.Fn sbwrite
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functions may fail and set
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.Va errno
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for 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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