Date: June 04, 2003
Description:
Manual page for libufs functions:
sbget(3)
sbsearch(3)
sbput(3)
sbread(3)
sbfind(3)
sbwrite(3)
This file is in the public domain.
.Dd August 8, 2022 .Dt SBREAD 3 .Os .Sh NAME .Nm sbget , sbsearch , sbput , sbread , sbfind , sbwrite .Nd read and write superblocks of a UFS file system .Sh LIBRARY .Lb libufs .Sh SYNOPSIS n sys/param.h n sys/mount.h n ufs/ufs/ufsmount.h n ufs/ufs/dinode.h n ufs/ffs/fs.h n libufs.h .Ft int .Fn sbget "int devfd" "struct fs **fsp" "off_t sblockloc" "int flags" .Ft int .Fn sbsearch "int devfd" "struct fs **fsp" "int flags" .Ft int .Fn sbput "int devfd" "struct fs *fs" "int numaltwrite" .Ft int .Fn sbread "struct uufsd *disk" .Ft int .Fn sbfind "struct uufsd *disk" "int flags" .Ft int .Fn sbwrite "struct uufsd *disk" "int all" .Sh DESCRIPTION The .Fn sbget , .Fn sbsearch , .Fn sbread , and .Fn sbfind functions provide superblock reads for .Xr libufs 3 consumers. The .Fn sbput and .Fn sbwrite functions provide superblock writes for .Xr libufs 3 consumers.
p The .Fn sbget and .Fn sbsearch functions first allocate a buffer to hold the superblock. Using the .Va devfd file descriptor that references the filesystem disk, .Fn sbget reads the superblock located at the byte offset specified by .Va sblockloc into the allocated buffer. The value .Cm UFS_STDSB may be specified for .Va sblockloc to request that the standard location for the superblock be read. The .Fn sbsearch function uses the .Va 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 .Fn sbsearch will attempt to find one of the filesystem's alternate superblocks. Flags are specified by .Em or Ns 'ing the following values:
p l -tag -width UFS_NOCSUM t Cm 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. t Cm UFS_NOMSG Indicates that superblock inconsistency error messages should not be printed. .El
p If successful, .Fn sbget and .Fn sbsearch functions return a pointer to the buffer containing the superblock in .Va fsp . The .Fn sbget and .Fn sbsearch functions are safe to use in threaded applications.
p The .Fn sbput function writes the superblock specified by .Va fs to the location from which it was read on the disk referenced by the .Va devfd file descriptor. Additionally, the .Fn sbput function will update the first .Va numaltwrite alternate superblock locations. To update all the alternate superblocks, specify a .Va numaltwrite value of .Va fs->fs_ncg . The .Fn sbput function is safe to use in threaded applications. Note that the .Fn sbput function needs to be called only if the superblock has been modified and the on-disk copy needs to be updated.
p The .Fn sbread function reads the standard filesystem superblock. The .Fn 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 .Fn sbfind will attempt to find one of the filesystem's alternate superblocks. If successful .Fn sbread and .Fn sbfind return a superblock in the .Va d_sb , structure embedded in the given user-land UFS disk structure.
p The .Fn sbwrite function writes the superblock from the .Va d_sb , structure embedded in the given user-land UFS disk structure to the location from which it was read. Additionally, the .Fn sbwrite function will write to all the alternate superblock locations if the .Fa all value is non-zero. .Sh RETURN VALUES .Rv -std sbread sbwrite The .Fn sbget , .Fn sbsearch , and .Fn sbput functions return the value 0 if successful; otherwise they return one of the errors described below. .Sh ERRORS The errors returned by .Fn sbget , .Fn sbsearch , .Fn sbread , and .Fn sbfind , include any of the errors specified for the library function .Xr bread 3 . Additionally, they may follow the .Xr libufs 3 error methodologies in situations where no usable superblock could be found.
p The errors returned by .Fn sbput and .Fn sbwrite include any of the errors specified for the library function .Xr bwrite 3 . .Sh SEE ALSO .Xr bread 3 , .Xr bwrite 3 , .Xr libufs 3 .Sh HISTORY These functions first appeared as part of .Xr libufs 3 in .Fx 5.0 . .Sh AUTHORS .An Juli Mallett Aq Mt jmallett@FreeBSD.org .An Marshall Kirk McKusick Aq Mt mckusick@FreeBSD.org