home | help 
CGREAD(3)		     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
     cgread()  function is equivalent to calling cgread1() with a cylinder group
     specifier equivalent to the value of the current d_ccg field, and then  in-
     crementing the d_ccg field.

     The  cgwrite()  function stores on disk the cylinder group held in the d_cg
     cylinder-group structure in a user-land UFS-disk structure.

     The cgwrite1() function provides no additional functionality over	the  cg-
     write() 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 func-
     tion  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).   Addition-
     ally  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 15.1			September 2, 2020		       CGREAD(3)
home | help