On Wed, Oct 17, 2012 at 10:36 PM, Eric Sandeen [off-list ref] wrote:

On 10/17/12 11:52 AM, Ashish Sangwan wrote:

quoted

Currently, e4defrag will not work on machines where /etc/mtab is not present
OR is empty.
This patch does 3 things:
a) Add option "-m mtab" to e4defrag so that user can specify any file to
be scanned for otbtaining mounted filesystems info.

Under what conditions would this be useful; i.e. when is mtab information
ever in a file other than /etc/mtab?

On embedded systems usually /etc is read-only. In that case /etc/mtab,
though  present, is empty.
When we tried to run e4defrag on our system, it gave segfault due to
the reasons mentioned in patch.

Then we look into xfs_fsr and found that it has this -m mtab option
due to which it worked without any problem
on our system. Also, xfs_fsr scans /proc/mounts first. So we changed
e4defrag accordingly.

Thanks,
-Eric

quoted

b) If mtab option is not specified, first we try to scan /proc/mounts, if failed
to access this file, we try with /etc/mtab.
c) In function is_ext4, check if the varibale "mnt_type" is null before
calling strcmp, otherwise segfault would occur if mtab is empty.

Signed-off-by: Ashish Sangwan <redacted>
Signed-off-by: Namjae Jeon <redacted>
---
 misc/e4defrag.8.in |   10 ++++++++++
 misc/e4defrag.c    |   34 ++++++++++++++++++++++------------
 2 files changed, 32 insertions(+), 12 deletions(-)

diff --git a/misc/e4defrag.8.in b/misc/e4defrag.8.in
index 75e1bc9..7090e51 100644
--- a/misc/e4defrag.8.in
+++ b/misc/e4defrag.8.in

@@ -9,6 +9,9 @@ e4defrag \- online defragmenter for ext4 filesystem
 [
 .B \-v
 ]
+[
+.B \-m mtab
+]
 .I target
 \&...
 .SH DESCRIPTION

@@ -57,6 +60,13 @@ is never defragmented.
 .B \-v
 Print error messages and the fragmentation count before and after defrag for
 each file.
+.TP
+.B \-m mtab
+This option will specify the file to be scanned for obtaining mounted filesystems
+information. If this option is not specified, the default is to use
+.B /proc/mounts .
+If this file is not accessible, e4defrag will try to get required information from
+.B /etc/mtab
 .SH NOTES
 .B e4defrag
 does not support swap file, files in lost+found directory, and files allocated

diff --git a/misc/e4defrag.c b/misc/e4defrag.c
index 4b31d03..3567e9f 100644
--- a/misc/e4defrag.c
+++ b/misc/e4defrag.c

@@ -123,6 +123,7 @@
 #define NGMSG_FILE_OPEN              "Failed to open"
 #define NGMSG_FILE_UNREG     "File is not regular file"
 #define NGMSG_LOST_FOUND     "Can not process \"lost+found\""
+#define _PATH_PROC_MOUNTS       "/proc/mounts"

 /* Data type for filesystem-wide blocks number */
 typedef unsigned long long ext4_fsblk_t;

@@ -262,10 +263,8 @@ static int fallocate64(int fd, int mode, loff_t offset, loff_t len)
  * @dir_path_len:    the length of directory.
  */
 static int get_mount_point(const char *devname, char *mount_point,
-                                                     int dir_path_len)
+                        int dir_path_len, const char *mtab)
 {
-     /* Refer to /etc/mtab */
-     const char      *mtab = MOUNTED;
      FILE            *fp = NULL;
      struct mntent   *mnt = NULL;
      struct stat64   sb;

@@ -278,7 +277,7 @@ static int get_mount_point(const char *devname, char *mount_point,

      fp = setmntent(mtab, "r");
      if (fp == NULL) {
-             perror("Couldn't access /etc/mtab");
+             printf("Couldn't access %s\n", mtab);
              return -1;
      }

@@ -313,14 +312,12 @@ static int get_mount_point(const char *devname, char *mount_point,
  *
  * @file:            the file's name.
  */
-static int is_ext4(const char *file, char *devname)
+static int is_ext4(const char *file, char *devname, const char *mtab)
 {
      int     maxlen = 0;
      int     len, ret;
      FILE    *fp = NULL;
      char    *mnt_type = NULL;
-     /* Refer to /etc/mtab */
-     const char      *mtab = MOUNTED;
      char    file_path[PATH_MAX + 1];
      struct mntent   *mnt = NULL;
      struct statfs64 fsbuf;

@@ -345,7 +342,7 @@ static int is_ext4(const char *file, char *devname)

      fp = setmntent(mtab, "r");
      if (fp == NULL) {
-             perror("Couldn't access /etc/mtab");
+             printf("Couldn't access %s", mtab);
              return -1;
      }

@@ -374,6 +371,10 @@ static int is_ext4(const char *file, char *devname)
      }

      endmntent(fp);
+     if (mnt_type == NULL) {
+             printf("Could not get mount information from %s\n", mtab);
+             return -1;
+     }
      if (strcmp(mnt_type, FS_EXT4) == 0) {
              FREE(mnt_type);
              return 0;

@@ -1724,6 +1725,7 @@ int main(int argc, char *argv[])
      int     success_flag = 0;
      char    dir_name[PATH_MAX + 1];
      char    dev_name[PATH_MAX + 1];
+     char *mtab = NULL;
      struct stat64   buf;
      ext2_filsys fs = NULL;

@@ -1731,7 +1733,7 @@ int main(int argc, char *argv[])
      if (argc == 1)
              goto out;

-     while ((opt = getopt(argc, argv, "vc")) != EOF) {
+     while ((opt = getopt(argc, argv, "vcm:")) != EOF) {
              switch (opt) {
              case 'v':
                      mode_flag |= DETAIL;

@@ -1739,11 +1741,19 @@ int main(int argc, char *argv[])
              case 'c':
                      mode_flag |= STATISTIC;
                      break;
+             case 'm':
+                     mtab = optarg;
+                     break;
              default:
                      goto out;
              }
      }
-
+     if (!mtab) {
+             if (access(_PATH_PROC_MOUNTS, R_OK) == 0)
+                     mtab = _PATH_PROC_MOUNTS;
+             else
+                     mtab = _PATH_MOUNTED;
+     }
      if (argc == optind)
              goto out;

@@ -1797,7 +1807,7 @@ int main(int argc, char *argv[])
              if (S_ISBLK(buf.st_mode)) {
                      /* Block device */
                      strncpy(dev_name, argv[i], strnlen(argv[i], PATH_MAX));
-                     if (get_mount_point(argv[i], dir_name, PATH_MAX) < 0)
+                     if (get_mount_point(argv[i], dir_name, PATH_MAX, mtab) < 0)
                              continue;
                      if (lstat64(dir_name, &buf) < 0) {
                              perror(NGMSG_FILE_INFO);

@@ -1833,7 +1843,7 @@ int main(int argc, char *argv[])
               * filesystem type checked in get_mount_point()
               */
              if (arg_type == FILENAME || arg_type == DIRNAME) {
-                     if (is_ext4(argv[i], dev_name) < 0)
+                     if (is_ext4(argv[i], dev_name, mtab) < 0)
                              continue;
                      if (realpath(argv[i], dir_name) == NULL) {
                              perror("Couldn't get full path");