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>

NEWS

@@ -24,6 +24,9 @@ GNU coreutils NEWS                                    -*- outline -*-
 
   sort now supports -d, -f, -i, -R, and -V in any combination.
 
+  stat now accepts the %m format directive to output
+  the mount point for a file.
+
 ** Changes in behavior
 
   df now consistently prints the device name for a bind mounted file,

THANKS

@@ -8,6 +8,7 @@ the bug-report mailing list (as seen on last line of e.g., cp --help).
 
 ???                                 kytek@cybercomm.net
 A Costa                             agcosta@gis.net
+Aaron Burgemeister                  dajoker@gmail.com
 Aaron Hawley                        ashawley@uvm.edu
 Achim Blumensath                    blume@corona.oche.de
 Adam Jimerson                       vendion@charter.net

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:
 

po/POTFILES.in

@@ -61,6 +61,7 @@ src/expand.c
 src/expr.c
 src/factor.c
 src/false.c
+src/find-mount-point.c
 src/fmt.c
 src/fold.c
 src/getlimits.c

src/Makefile.am

@@ -145,6 +145,7 @@ noinst_HEADERS =	\
   copy.h		\
   cp-hash.h		\
   dircolors.h		\
+  find-mount-point.h	\
   fs.h			\
   group-list.h		\
   ls.h			\
@@ -478,6 +479,9 @@ rm_SOURCES = rm.c remove.c
 mkdir_SOURCES = mkdir.c prog-fprintf.c
 rmdir_SOURCES = rmdir.c prog-fprintf.c
 
+df_SOURCES = df.c find-mount-point.c
+stat_SOURCES = stat.c find-mount-point.c
+
 uname_SOURCES = uname.c uname-uname.c
 arch_SOURCES = uname.c uname-arch.c
 nproc_SOURCES = nproc.c

src/df.c

@@ -29,8 +29,7 @@
 #include "human.h"
 #include "mountlist.h"
 #include "quote.h"
-#include "save-cwd.h"
-#include "xgetcwd.h"
+#include "find-mount-point.h"
 
 /* The official name of this program (e.g., no `g' prefix).  */
 #define PROGRAM_NAME "df"
@@ -522,94 +521,6 @@ show_dev (char const *disk, char const *mount_point,
   putchar ('\n');
 }
 
-/* Return the root mountpoint of the file system on which FILE exists, in
-   malloced storage.  FILE_STAT should be the result of stating FILE.
-   Give a diagnostic and return NULL if unable to determine the mount point.
-   Exit if unable to restore current working directory.  */
-static char *
-find_mount_point (const char *file, const struct stat *file_stat)
-{
-  struct saved_cwd cwd;
-  struct stat last_stat;
-  char *mp = NULL;		/* The malloced mount point.  */
-
-  if (save_cwd (&cwd) != 0)
-    {
-      error (0, errno, _("cannot get current directory"));
-      return NULL;
-    }
-
-  if (S_ISDIR (file_stat->st_mode))
-    /* FILE is a directory, so just chdir there directly.  */
-    {
-      last_stat = *file_stat;
-      if (chdir (file) < 0)
-        {
-          error (0, errno, _("cannot change to directory %s"), quote (file));
-          return NULL;
-        }
-    }
-  else
-    /* FILE is some other kind of file; use its directory.  */
-    {
-      char *xdir = dir_name (file);
-      char *dir;
-      ASSIGN_STRDUPA (dir, xdir);
-      free (xdir);
-
-      if (chdir (dir) < 0)
-        {
-          error (0, errno, _("cannot change to directory %s"), quote (dir));
-          return NULL;
-        }
-
-      if (stat (".", &last_stat) < 0)
-        {
-          error (0, errno, _("cannot stat current directory (now %s)"),
-                 quote (dir));
-          goto done;
-        }
-    }
-
-  /* Now walk up FILE's parents until we find another file system or /,
-     chdiring as we go.  LAST_STAT holds stat information for the last place
-     we visited.  */
-  while (true)
-    {
-      struct stat st;
-      if (stat ("..", &st) < 0)
-        {
-          error (0, errno, _("cannot stat %s"), quote (".."));
-          goto done;
-        }
-      if (st.st_dev != last_stat.st_dev || st.st_ino == last_stat.st_ino)
-        /* cwd is the mount point.  */
-        break;
-      if (chdir ("..") < 0)
-        {
-          error (0, errno, _("cannot change to directory %s"), quote (".."));
-          goto done;
-        }
-      last_stat = st;
-    }
-
-  /* Finally reached a mount point, see what it's called.  */
-  mp = xgetcwd ();
-
-done:
-  /* Restore the original cwd.  */
-  {
-    int save_errno = errno;
-    if (restore_cwd (&cwd) != 0)
-      error (EXIT_FAILURE, errno,
-             _("failed to return to initial working directory"));
-    free_cwd (&cwd);
-    errno = save_errno;
-  }
-
-  return mp;
-}
-
 /* If DISK corresponds to a mount point, show its usage
    and return true.  Otherwise, return false.  */
 static bool

src/find-mount-point.c

@@ -0,0 +1,113 @@
+/* find-mount-point.c -- find the root mount point for a file.
+   Copyright (C) 2010 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <config.h>
+#include <sys/types.h>
+
+#include "system.h"
+#include "error.h"
+#include "quote.h"
+#include "save-cwd.h"
+#include "xgetcwd.h"
+#include "find-mount-point.h"
+
+/* Return the root mountpoint of the file system on which FILE exists, in
+   malloced storage.  FILE_STAT should be the result of stating FILE.
+   Give a diagnostic and return NULL if unable to determine the mount point.
+   Exit if unable to restore current working directory.  */
+extern char *
+find_mount_point (const char *file, const struct stat *file_stat)
+{
+  struct saved_cwd cwd;
+  struct stat last_stat;
+  char *mp = NULL;		/* The malloced mount point.  */
+
+  if (save_cwd (&cwd) != 0)
+    {
+      error (0, errno, _("cannot get current directory"));
+      return NULL;
+    }
+
+  if (S_ISDIR (file_stat->st_mode))
+    /* FILE is a directory, so just chdir there directly.  */
+    {
+      last_stat = *file_stat;
+      if (chdir (file) < 0)
+        {
+          error (0, errno, _("cannot change to directory %s"), quote (file));
+          return NULL;
+        }
+    }
+  else
+    /* FILE is some other kind of file; use its directory.  */
+    {
+      char *xdir = dir_name (file);
+      char *dir;
+      ASSIGN_STRDUPA (dir, xdir);
+      free (xdir);
+
+      if (chdir (dir) < 0)
+        {
+          error (0, errno, _("cannot change to directory %s"), quote (dir));
+          return NULL;
+        }
+
+      if (stat (".", &last_stat) < 0)
+        {
+          error (0, errno, _("cannot stat current directory (now %s)"),
+                 quote (dir));
+          goto done;
+        }
+    }
+
+  /* Now walk up FILE's parents until we find another file system or /,
+     chdiring as we go.  LAST_STAT holds stat information for the last place
+     we visited.  */
+  while (true)
+    {
+      struct stat st;
+      if (stat ("..", &st) < 0)
+        {
+          error (0, errno, _("cannot stat %s"), quote (".."));
+          goto done;
+        }
+      if (st.st_dev != last_stat.st_dev || st.st_ino == last_stat.st_ino)
+        /* cwd is the mount point.  */
+        break;
+      if (chdir ("..") < 0)
+        {
+          error (0, errno, _("cannot change to directory %s"), quote (".."));
+          goto done;
+        }
+      last_stat = st;
+    }
+
+  /* Finally reached a mount point, see what it's called.  */
+  mp = xgetcwd ();
+
+done:
+  /* Restore the original cwd.  */
+  {
+    int save_errno = errno;
+    if (restore_cwd (&cwd) != 0)
+      error (EXIT_FAILURE, errno,
+             _("failed to return to initial working directory"));
+    free_cwd (&cwd);
+    errno = save_errno;
+  }
+
+  return mp;
+}

src/find-mount-point.h

@@ -0,0 +1,17 @@
+/* find-mount-point.h -- find the root mount point for a file.
+   Copyright (C) 2010 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+extern char* find_mount_point (const char *, const struct stat *);