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Date: Thu, 18 Oct 2012 08:27:50 +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 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.
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
>
>> 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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