175 lines
3.6 KiB
Groff
175 lines
3.6 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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.\" cgget(3)
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.\" cgput(3)
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.\" cgread(3)
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.\" cgread1(3)
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.\" cgwrite(3)
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.\" cgwrite1(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 CGREAD 3
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.Os
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.Sh NAME
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.Nm cgget , cgput , cgread , cgread1 , cgwrite , cgwrite1
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.Nd read/write cylinder groups of UFS disks
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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 cgget "struct uufsd *disk" "int cg" "struct cg *cgp"
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.Ft int
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.Fn cgput "struct uufsd *disk" "struct cg *cgp"
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.Ft int
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.Fn cgread "struct uufsd *disk"
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.Ft int
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.Fn cgread1 "struct uufsd *disk" "int cg"
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.Ft int
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.Fn cgwrite "struct uufsd *disk"
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.Ft int
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.Fn cgwrite1 "struct uufsd *disk" "int cg"
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.Sh DESCRIPTION
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The
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.Fn cgget ,
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.Fn cgread ,
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and
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.Fn cgread1
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functions provide cylinder group reads for
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.Xr libufs 3
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consumers.
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The
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.Fn cgput ,
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.Fn cgwrite ,
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and
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.Fn cgwrite1
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functions provide cylinder group 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 cgget
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function reads the cylinder group specified by
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.Fa cg
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into the buffer pointed to by
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.Fa cgp
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from the disk referenced by the user-land UFS-disk structure.
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The
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.Fn cgget
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function is the only cylinder group read function that is safe to use
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in threaded applications.
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.Pp
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The
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.Fn cgput
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function writes the cylinder group specified by
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.Va cgp
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to the disk referenced by the user-land UFS-disk structure.
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The
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.Fn cgput
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function is the only cylinder group write function that is safe to use
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in threaded applications.
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Note that the
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.Fn cgput
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function needs to be called only if the cylinder group 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 cgread1
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function reads from the cylinder group specified by
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.Fa cg
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into the
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.Va d_cg
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cylinder-group structure in a user-land UFS-disk structure.
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It sets the
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.Va d_lcg
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field to the cylinder group number
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.Fa cg .
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.Pp
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The
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.Fn cgread
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function operates on sequential cylinder groups.
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Calling the
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.Fn cgread
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function is equivalent to calling
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.Fn cgread1
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with a cylinder group specifier equivalent to the value of the current
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.Va d_ccg
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field, and then incrementing the
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.Va d_ccg
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field.
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.Pp
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The
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.Fn cgwrite
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function stores on disk the cylinder group held in the
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.Va d_cg
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cylinder-group structure in a user-land UFS-disk structure.
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.Pp
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The
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.Fn cgwrite1
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function provides no additional functionality over the
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.Fn cgwrite
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function as there is only one place that a given cylinder group
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can correctly be written.
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If the caller gets the
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.Fa cg
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parameter wrong, the function fails with the error
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.Er EDOOFUS .
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This function remains only to provide backward compatibility.
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.Sh RETURN VALUES
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The
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.Fn cgread
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function returns 0 if there are no more cylinder groups to read,
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1 if there are more cylinder groups, and \-1 on error.
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The
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.Fn cgread1
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function returns 1 on success and \-1 on error.
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The other functions return 0 on success and \-1 on error.
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.Sh ERRORS
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The
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.Fn cgget ,
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.Fn cgread ,
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and
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.Fn cgread1
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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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.Pp
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The
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.Fn cgput ,
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.Fn cgwrite ,
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and
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.Fn cgwrite1
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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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Additionally the
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.Fn cgwrite1
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will return the
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.Er EDOOFUS
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error if the cylinder group specified does not match the
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cylinder group that it is requesting to write.
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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 5.1 .
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.Sh AUTHORS
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.An Juli Mallett Aq Mt jmallett@FreeBSD.org
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