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

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On Thu, Oct 18, 2012 at 8:30 AM, Eric Sandeen <sandeen@xxxxxxxxxx> wrote:
> On 10/17/12 9:57 PM, Ashish Sangwan wrote:
>> On Wed, Oct 17, 2012 at 10:36 PM, Eric Sandeen <sandeen@xxxxxxxxxx> 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.
>
you are right. Actually xfs_fsr may work on more than 1 mounted XFS
filesystem in a single run.
That is why it makes _little_ sense for xfs_fsr to have this mtab
option so that user can provide
exclusive mounted xfs partitions info in a seprate file.
But e4defrag would work on a single mounted partition in a single run.
This won't be much helpful here if not for compatiblity.

> 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@xxxxxxxxx>
>>>> Signed-off-by: Namjae Jeon <linkinjeon@xxxxxxxxx>
>>>> ---
>>>>  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");
>>>>
>>>
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