document fat permissions a little better, based on some notes from martynas

feedback/ok sobrado martynas

1 files changed, 45 insertions, 22 deletions

diff --git a/sbin/mount_msdos/mount_msdos.8 b/sbin/mount_msdos/mount_msdos.8
index ccc0d1beff0..3e7a00fc814 100644
--- a/sbin/mount_msdos/mount_msdos.8
+++ b/sbin/mount_msdos/mount_msdos.8
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: mount_msdos.8,v 1.24 2009/08/07 19:27:27 martynas Exp $
+.\"	$OpenBSD: mount_msdos.8,v 1.25 2009/08/09 06:45:49 jmc Exp $
 .\"	$NetBSD: mount_msdos.8,v 1.10 1996/01/19 21:14:43 leo Exp $
 .\"
 .\" Copyright (c) 1993,1994 Christopher G. Demetriou
@@ -29,7 +29,7 @@
 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd $Mdocdate: August 7 2009 $
+.Dd $Mdocdate: August 9 2009 $
 .Dt MOUNT_MSDOS 8
 .Os
 .Sh NAME
@@ -47,10 +47,10 @@
 .Sh DESCRIPTION
 The
 .Nm
-command attaches the MS-DOS filesystem residing on
+command attaches the MS-DOS file system residing on
 the device
 .Ar special
-to the global filesystem namespace at the location
+to the global file system namespace at the location
 indicated by
 .Ar node .
 This command is invoked by
@@ -97,7 +97,7 @@ nor
 .Fl l
 are given,
 .Nm
-searches the root directory of the filesystem to
+searches the root directory of the file system to
 be mounted for any existing Windows 95/98 long filenames.
 If no such entries are found,
 .Fl s
@@ -108,19 +108,9 @@ is assumed.
 .It Fl m Ar mask
 Specify the maximum permissions for files and directories
 in the file system.
-(For example, a mask of
-.Li 755
-specifies that, by default, the owner should have
-read, write, and execute permissions, but
-others should only have read and execute permissions.
-See
-.Xr chmod 1
-for more information about octal file modes.)
 Only the nine low-order bits of
 .Ar mask
 are used.
-The default mask is taken from the
-directory on which the file system is being mounted.
 .It Fl o Ar options
 Use the specified mount
 .Ar options ,
@@ -136,7 +126,7 @@ nor
 .Fl l
 are given,
 .Nm
-searches the root directory of the filesystem to
+searches the root directory of the file system to
 be mounted for any existing Windows 95/98 long filenames.
 If no such entries are found,
 .Fl s
@@ -152,7 +142,40 @@ on which the file system is being mounted.
 .It Fl x
 If a directory is readable, it inherits the x attribute as well.
 .El
+.Pp
+File permissions for FAT file systems are imitated,
+since the file system has no real concept of permissions.
+The default mask is taken from the
+directory on which the file system is being mounted,
+except when the
+.Fl m
+option is used.
+FAT does have a
+.Dq read only
+mode,
+in which the writable bit is unset.
+If such files are found,
+they are marked non-writable;
+it can be set using
+.Li chmod -w
+or unset using
+.Li chmod +w .
+.Pp
+File modes work the same way for directories.
+However if a directory is mounted with
+.Fl x ,
+it will inherit the executable bit if it is readable.
+This can be useful for making files non-executable
+and directories executable:
+using
+.Li -x -m 644
+will in most cases give permissions of 755 for directories
+and 644 for files.
+See
+.Xr chmod 1
+for more information about octal file modes.
 .Sh SEE ALSO
+.Xr chmod 1 ,
 .Xr mount 2 ,
 .Xr disklabel 5 ,
 .Xr fstab 5 ,
@@ -172,20 +195,20 @@ and was abandoned in favor
 of the more aptly named
 .Nm mount_msdos .
 .Sh CAVEATS
-The maximum file size supported by the MS-DOS filesystem is
+The maximum file size supported by the MS-DOS file system is
 one byte less than 4GB.
-This is a FAT filesystem limitation, documented by Microsoft
+This is a FAT file system limitation, documented by Microsoft
 in Knowledge Base article 314463.
 .Pp
-The MS-DOS filesystem (even with long filenames) does not support
+The MS-DOS file system (even with long filenames) does not support
 filenames with trailing dots or spaces.
 Any such characters will be silently removed before the directory entry
 is written.
-This too is a FAT filesystem limitation.
+This too is a FAT file system limitation.
 .Pp
 The use of the
 .Fl 9
-flag could result in damaged filesystems,
+flag could result in damaged file systems,
 albeit the damage is in part taken care of by
 procedures similar to the ones used in Windows 95/98.
 .Pp
@@ -193,7 +216,7 @@ The default handling for
 .Fl s
 and
 .Fl l
-will result in empty filesystems being populated
+will result in empty file systems being populated
 with short filenames only.
 To generate long filenames on empty DOS file systems use
 .Fl l .