stat: add %m to output the mount point for a file

* src/find-mount-point.c: A new file refactoring
find_mount_point() out from df.c
* src/find-mount-point.h: Likewise.
* src/df.c: Use the new find-mount-point module.
* src/stat.c (print_stat): Handle the new %m format.
(find_bind_mount): A new function to
return the bind mount for a file if any.
(out_mount_mount): Print the bind mount for a file, or else
the standard mount point given by the find-mount-point module.
(usage): Document the %m format directive.
* src/Makefile.am: Reference the refactored find-mount-point.c
* po/POTFILES.in: Add find_mount_point.c to the translation list
* doc/coreutils.texi (stat invocation): Document %m,
and how it may differ from the mount point that df outputs.
* test/misc/stat-mount: A new test to correlate mount points
output from df and stat.
* tests/Makefile.am: Reference the new test.
* NEWS: Mention the new feature
* THANKS: Add the author

Signed-off-by: Pádraig Brady <P@draigBrady.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index 7eedec75a..6771da949 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -8487,6 +8487,7 @@ removal is requested.  Equivalent to @option{-I}.
 When removing a hierarchy recursively, skip any directory that is on a
 file system different from that of the corresponding command line argument.
 
+@cindex bind mount
 This option is useful when removing a build ``chroot'' hierarchy,
 which normally contains no valuable data.  However, it is not uncommon
 to bind-mount @file{/home} into such a hierarchy, to make it easier to
@@ -10685,6 +10686,7 @@ The valid @var{format} directives for files with @option{--format} and
 @item %G - Group name of owner
 @item %h - Number of hard links
 @item %i - Inode number
+@item %m - Mount point (See note below)
 @item %n - File name
 @item %N - Quoted file name with dereference if symbolic link
 @item %o - I/O block size
@@ -10701,6 +10703,22 @@ The valid @var{format} directives for files with @option{--format} and
 @item %Z - Time of last change as seconds since Epoch
 @end itemize
 
+The mount point printed by @samp{%m} is similar to that output
+by @command{df}, except that:
+@itemize @bullet
+@item
+stat does not dereference symlinks by default
+(unless @option{-L} is specified)
+@item
+stat does not search for specified device nodes in the
+file system list, instead operating on them directly
+@item
+@cindex bind mount
+stat outputs the alias for a bind mounted file,
+rather than its backing device.  One can recursively call stat
+until there is no change in output, to get the base mount point
+@end itemize
+
 When listing file system information (@option{--file-system} (@option{-f})),
 you must use a different set of @var{format} directives: