Index: head/lib/libufs/sbread.3
===================================================================
--- head/lib/libufs/sbread.3	(revision 362559)
+++ head/lib/libufs/sbread.3	(revision 362560)
@@ -1,145 +1,147 @@
 .\" Author:	Juli Mallett <jmallett@FreeBSD.org>
 .\" Date:	June 04, 2003
 .\" Description:
 .\" 	Manual page for libufs functions:
 .\"		sbget(3)
 .\"		sbput(3)
 .\"		sbread(3)
 .\"		sbwrite(3)
 .\"
 .\" This file is in the public domain.
 .\"
 .\" $FreeBSD$
 .\"
 .Dd January 19, 2018
 .Dt SBREAD 3
 .Os
 .Sh NAME
 .Nm sbget , sbput , sbread , sbwrite
 .Nd read and write superblocks of a UFS file system
 .Sh LIBRARY
 .Lb libufs
 .Sh SYNOPSIS
 .In sys/param.h
 .In sys/mount.h
 .In ufs/ufs/ufsmount.h
 .In ufs/ufs/dinode.h
 .In ufs/ffs/fs.h
 .In libufs.h
 .Ft int
 .Fn sbget "int devfd" "struct fs **fsp" "off_t sblockloc"
 .Ft int
 .Fn sbput "int devfd" "struct fs *fs" "int numaltwrite"
 .Ft int
 .Fn sbread "struct uufsd *disk"
 .Ft int
 .Fn sbwrite "struct uufsd *disk" "int all"
 .Sh DESCRIPTION
 The
 .Fn sbget
 and
 .Fn sbread
 functions provide superblock reads for
 .Xr libufs 3
 consumers.
 The
 .Fn sbput
 and
 .Fn sbwrite
 functions provide superblock writes for
 .Xr libufs 3
 consumers.
 .Pp
 The
 .Fn sbget
 function first allocates 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.
 If successful, it returns a pointer to the buffer containing the superblock in
 .Va fsp .
 The
 .Fn sbget
 function is safe to use in threaded applications.
 .Pp
 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.
 .Pp
 The
 .Fn sbread
 function reads the standard filesystem superblock into the
 .Va d_sb ,
 structure embedded in the given user-land UFS disk structure.
 .Pp
 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 sbget sbput sbread sbwrite
-.Sh ERRORS
+.Rv -std sbread sbwrite
 The
 .Fn sbget
 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
+and
 .Fn sbread
-functions may fail and set
-.Va errno
-for any of the errors specified for the library function
+include any of the errors specified for the library function
 .Xr bread 3 .
-Additionally, it may follow the
+Additionally, they may follow the
 .Xr libufs 3
 error methodologies in situations where no usable superblock could be
 found.
 .Pp
-The
+The errors returned by
 .Fn sbput
 and
 .Fn sbwrite
-functions may fail and set
-.Va errno
-for any of the errors specified for the library function
+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