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CGREAD(3) FreeBSD Library Functions Manual CGREAD(3) NAME cgget, cgput, cgread, cgread1, cgwrite, cgwrite1 - read/write cylinder groups of UFS disks 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 cgget(int devfd, struct fs *fs, int cg, struct cg *cgp); int cgput(int devfd, struct fs *fs, struct cg *cgp); int cgread(struct uufsd *disk); int cgread1(struct uufsd *disk, int cg); int cgwrite(struct uufsd *disk); int cgwrite1(struct uufsd *disk, int cg); DESCRIPTION The cgget(), cgread(), and cgread1() functions provide cylinder group reads for libufs(3) consumers. The cgput(), cgwrite(), and cgwrite1() functions provide cylinder group writes for libufs(3) consumers. The cgget() function reads the cylinder group specified by cg into the buffer pointed to by cgp from the filesystem described by the fs superblock using the devfd file descriptor that references the filesystem disk. The cgget() function is the only cylinder group read function that is safe to use in threaded applications. The cgput() function writes the cylinder group specified by cgp to the filesystem described by the fs superblock using the devfd file descriptor that references the filesystem disk. The cgput() function is the only cylinder group write function that is safe to use in threaded applications. Note that the cgput() function needs to be called only if the cylinder group has been modified and the on-disk copy needs to be updated. The cgread1() function reads from the cylinder group specified by cg into the d_cg cylinder-group structure in a user-land UFS-disk structure. It sets the d_lcg field to the cylinder group number cg. The cgread() function operates on sequential cylinder groups. Calling The cgwrite1() function provides no additional functionality over the cgwrite() function as there is only one place that a given cylinder group can correctly be written. If the caller gets the cg parameter wrong, the function fails with the error EDOOFUS. This function remains only to provide backward compatibility. RETURN VALUES The cgread() function returns 0 if there are no more cylinder groups to read, 1 if there are more cylinder groups, and -1 on error. The cgread1() function returns 1 on success and -1 on error. The other functions return 0 on success and -1 on error. ERRORS The cgget(), cgread(), and cgread1() functions may fail and set errno for any of the errors specified for the library function bread(3). The cgput(), cgwrite(), and cgwrite1() functions may fail and set errno for any of the errors specified for the library function bwrite(3). Additionally the cgwrite1() will return the EDOOFUS error if the cylinder group specified does not match the cylinder group that it is requesting to write. SEE ALSO bread(3), bwrite(3), libufs(3) HISTORY These functions first appeared as part of libufs(3) in FreeBSD 5.1. AUTHORS Juli Mallett <jmallett@FreeBSD.org> Marshall Kirk McKusick <mckusick@FreeBSD.org> FreeBSD 14.0-RELEASE-p6 September 2, 2020 FreeBSD 14.0-RELEASE-p6