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Date: Thu, 18 Oct 2012 08:39:49 +0530
From: Ashish Sangwan <ashishsangwan2@...il.com>
To: Eric Sandeen <sandeen@...hat.com>
Cc: tytso@....edu, linux-ext4@...r.kernel.org,
Namjae Jeon <linkinjeon@...il.com>
Subject: Re: [PATCH] e4defrag: Add option -m mtab to e4defrag
On Thu, Oct 18, 2012 at 8:30 AM, Eric Sandeen <sandeen@...hat.com> wrote:
> On 10/17/12 9:57 PM, Ashish Sangwan wrote:
>> On Wed, Oct 17, 2012 at 10:36 PM, Eric Sandeen <sandeen@...hat.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.
>
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@...il.com>
>>>> Signed-off-by: Namjae Jeon <linkinjeon@...il.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");
>>>>
>>>
>> --
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