Re: [PATCH] e4defrag: Add option -m mtab to e4defrag

[Eric Sandeen <sandeen@redhat.com>]

On 10/17/12 9:57 PM, Ashish Sangwan wrote:
> On Wed, Oct 17, 2012 at 10:36 PM, Eric Sandeen <sandeen@redhat.com> wrote:
>> On 10/17/12 11:52 AM, Ashish Sangwan wrote:
>>> 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.

Clearly the segfault needs to be fixed, and looking at /proc/mounts makes sense.
But I just wonder about the usefulness of being able to specify an arbitrary
file in lieu of /etc/mtab.  Unless there's a clear usecase I'm not sure I'd
add it.

> 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.

Compatibility with xfs_fsr is the only reason I can think of to do it :)

I just can't imagine why mount information would be anywhere other than
/etc/mtab or /proc/mounts.

Just pushing back on the complexity a little.

Thanks,
-Eric

>> Thanks,
>> -Eric
>>
>>> 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 <ashish.sangwan2@gmail.com>
>>> Signed-off-by: Namjae Jeon <linkinjeon@gmail.com>
>>> ---
>>>  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");
>>>
>>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>