[PATCH] xfs_fsr: use /proc/mounts if available

[Christoph Hellwig <hch@xxxxxxxxxxxxx>]

Prefer /proc/mounts if it exists over /etc/mtab to get a correct picture
of the kernels mount table for this process.  This works arounds some
userspace like pam_mount polluting /etc/mtab with incorrect entries.

Also remove the "mtab" global variable and instead pass it explicitly
to fsrallfs, like we already do for other functions.

Signed-off-by: Christoph Hellwig <hch@xxxxxx>

Index: xfsprogs-dev/fsr/xfs_fsr.c
===================================================================
--- xfsprogs-dev.orig/fsr/xfs_fsr.c     2010-09-11 20:06:15.000000000 +0000
+++ xfsprogs-dev/fsr/xfs_fsr.c  2010-09-12 16:28:17.000000000 +0000
@@ -42,7 +42,9 @@
 #define XFS_XFLAG_NODEFRAG 0x00002000 /* src dependancy, remove later */
 #endif
 
-#define _PATH_FSRLAST  "/var/tmp/.fsrlast_xfs"
+#define _PATH_FSRLAST          "/var/tmp/.fsrlast_xfs"
+#define _PATH_PROC_MOUNTS      "/proc/mounts"
+
 
 char *progname;
 
@@ -79,7 +81,6 @@ static __int64_t      minimumfree = 2048;
 
 static time_t howlong = 7200;          /* default seconds of reorganizing */
 static char *leftofffile = _PATH_FSRLAST; /* where we left off last */
-static char *mtab = MOUNTED;
 static time_t endtime;
 static time_t starttime;
 static xfs_ino_t       leftoffino = 0;
@@ -94,7 +95,7 @@ static int  packfile(char *fname, char *
 static void fsrdir(char *dirname);
 static int  fsrfs(char *mntdir, xfs_ino_t ino, int targetrange);
 static void initallfs(char *mtab);
-static void fsrallfs(int howlong, char *leftofffile);
+static void fsrallfs(char *mtab, int howlong, char *leftofffile);
 static void fsrall_cleanup(int timeout);
 static int  getnextents(int);
 int xfsrtextsize(int fd);
@@ -187,6 +188,7 @@ main(int argc, char **argv)
        struct mntent mntpref;
        register struct mntent *mntp;
        struct mntent ment;
+       char *mtab = NULL;
        register FILE *mtabp;
 
        setlinebuf(stdout);
@@ -198,7 +200,7 @@ main(int argc, char **argv)
 
        gflag = ! isatty(0);
 
-       while ((c = getopt(argc, argv, "C:p:e:MgsdnvTt:f:m:b:N:FV")) != -1 )
+       while ((c = getopt(argc, argv, "C:p:e:MgsdnvTt:f:m:b:N:FV")) != -1) {
                switch (c) {
                case 'M':
                        Mflag = 1;
@@ -250,6 +252,22 @@ main(int argc, char **argv)
                default:
                        usage(1);
                }
+       }
+
+       /*
+        * If the user did not specify an explicit mount table, try to use
+        * /proc/mounts if it is available, else /etc/mtab.  We prefer
+        * /proc/mounts because it is kernel controlled, while /etc/mtab
+        * may contain garbage that userspace tools like pam_mounts wrote
+        * into it.
+        */
+       if (!mtab) {
+               if (access(_PATH_PROC_MOUNTS, R_OK) == 0)
+                       mtab = _PATH_PROC_MOUNTS;
+               else
+                       mtab = _PATH_MOUNTED;
+       }
+
        if (vflag)
                setbuf(stdout, NULL);
 
@@ -330,7 +348,7 @@ main(int argc, char **argv)
                }
        } else {
                initallfs(mtab);
-               fsrallfs(howlong, leftofffile);
+               fsrallfs(mtab, howlong, leftofffile);
        }
        return 0;
 }
@@ -447,7 +465,7 @@ initallfs(char *mtab)
 }
 
 static void
-fsrallfs(int howlong, char *leftofffile)
+fsrallfs(char *mtab, int howlong, char *leftofffile)
 {
        int fd;
        int error;