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SBREAD(3) FreeBSD Library Functions Manual SBREAD(3)
NAME
sbget, sbsearch, sbput, sbread, sbfind, sbwrite - read and write
superblocks of a UFS file system
LIBRARY
UFS File System Access Library (libufs, -lufs)
SYNOPSIS
#include <sys/param.h>
#include <sys/mount.h>
#include <ufs/ufs/ufsmount.h>
#include <ufs/ufs/dinode.h>
#include <ufs/ffs/fs.h>
#include <libufs.h>
int
sbget(int devfd, struct fs **fsp, off_t sblockloc, int flags);
int
sbsearch(int devfd, struct fs **fsp, int flags);
int
sbput(int devfd, struct fs *fs, int numaltwrite);
int
sbread(struct uufsd *disk);
int
sbfind(struct uufsd *disk, int flags);
int
sbwrite(struct uufsd *disk, int all);
DESCRIPTION
The sbget(), sbsearch(), sbread(), and sbfind() functions provide
superblock reads for libufs(3) consumers. The sbput() and sbwrite()
functions provide superblock writes for libufs(3) consumers.
The sbget() and sbsearch() functions first allocate a buffer to hold the
superblock. Using the devfd file descriptor that references the
filesystem disk, sbget() reads the superblock located at the byte offset
specified by sblockloc into the allocated buffer. The value UFS_STDSB
may be specified for sblockloc to request that the standard location for
the superblock be read. The sbsearch() function uses the devfd file
descriptor that references the filesystem disk, to search first for the
superblock at the standard location. If it is not found or is too
damaged to use sbsearch() will attempt to find one of the filesystem's
alternate superblocks. Flags are specified by or'ing the following
values:
UFS_NOCSUM Causes only the superblock itself to be returned, but does
not read in any auxiliary data structures like the cylinder
group summary information.
UFS_NOMSG Indicates that superblock inconsistency error messages should
not be printed.
numaltwrite alternate superblock locations. To update all the alternate
superblocks, specify a numaltwrite value of fs->fs_ncg. The sbput()
function is safe to use in threaded applications. Note that the sbput()
function needs to be called only if the superblock has been modified and
the on-disk copy needs to be updated.
The sbread() function reads the standard filesystem superblock. The
sbfind() function tries to find a usable superblock. It searchs first
for the superblock at the standard location. If it is not found or is
too damaged to use sbfind() will attempt to find one of the filesystem's
alternate superblocks. If successful sbread() and sbfind() return a
superblock in the d_sb, structure embedded in the given user-land UFS
disk structure.
The sbwrite() function writes the superblock from the d_sb, structure
embedded in the given user-land UFS disk structure to the location from
which it was read. Additionally, the sbwrite() function will write to
all the alternate superblock locations if the all value is non-zero.
RETURN VALUES
The sbread() and sbwrite() functions return the value 0 if successful;
otherwise the value -1 is returned and the global variable errno is set
to indicate the error. The sbget(), sbsearch(), and sbput() functions
return the value 0 if successful; otherwise they return one of the errors
described below.
ERRORS
The errors returned by sbget(), sbsearch(), sbread(), and sbfind(),
include any of the errors specified for the library function bread(3).
Additionally, they may follow the libufs(3) error methodologies in
situations where no usable superblock could be found.
The errors returned by sbput() and sbwrite() include any of the errors
specified for the library function bwrite(3).
SEE ALSO
bread(3), bwrite(3), libufs(3)
HISTORY
These functions first appeared as part of libufs(3) in FreeBSD 5.0.
AUTHORS
Juli Mallett <jmallett@FreeBSD.org>
Marshall Kirk McKusick <mckusick@FreeBSD.org>
FreeBSD 14.0-RELEASE-p6 August 8, 2022 FreeBSD 14.0-RELEASE-p6