Re: modify chmod (original) (raw)

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From:	jeff.liu
Subject:	Re: modify chmod
Date:	Mon, 08 Feb 2010 21:58:43 +0800
User-agent:	Thunderbird 2.0.0.14 (X11/20080505)

Jim Meyering 写道:

Finally, I see the one true way ;-) Do this for each "name":

- open each file/dir. with fd = openat (ftscwdfd, name, ... - if that succeeds, then call fstatfs (fd, ...

Using the combination of openat and fstatfs is required in order to avoid using the full relative name of each object that chmod processes.

The above works for all readable objects. For unreadable ones, revert to using the statfs with the full relative name.

Thanks for the hints.

But according to my tryout, it looks we can not gain performance benefits in this way. :( calling openat() could cause a bits overhead as well.

I have done a simple test against a directory mounted as ext3 fs, set its default permission bits to 644.

address@hidden:/ocfs2# du -sh . 2.0G .

address@hidden:/ocfs2# ls -ld . drw-r--r-- 8 root root 4096 Feb 8 16:11 .

address@hidden:~/opensource_dev/coreutils$ time yes | sudo ./src/chmod -R 644 /ocfs2/

real 0m16.421s user 0m0.400s sys 0m15.605s

address@hidden:~/opensource_dev/coreutils$ time yes | sudo ./src/chmod -R 755 /ocfs2/

real 0m17.129s user 0m0.308s sys 0m16.233s

address@hidden:~/opensource_dev/coreutils$ time yes | sudo ./src/chmod -R 755 /ocfs2/

real 0m17.029s user 0m0.400s sys 0m16.157s

Could you check the following patch, hope I didn't misunderstood your idea.

From ec84e84d79a69d1422e0d02ab99a65c30c75b27f Mon Sep 17 00:00:00 2001 From: Jie Liu <address@hidden> Date: Mon, 8 Feb 2010 16:51:37 +0800 Subject: [PATCH] chmod modify: do not touch inode for same permission bits v2

This patch change the chmod default behavior to skip chmodat(2) the inode if its new permission bits is same as it was before.

Signed-off-by: Jie Liu <address@hidden>

src/chmod.c | 87 ++++++++++++++++++++++++++++++++++++++++++++++++++++++----- 1 files changed, 80 insertions(+), 7 deletions(-)

diff --git a/src/chmod.c b/src/chmod.c index 3dab92e..b49adb8 100644 --- a/src/chmod.c +++ b/src/chmod.c @@ -20,6 +20,7 @@ #include <stdio.h> #include <getopt.h> #include <sys/types.h> +#include <unistd.h>

#include "system.h" #include "dev-ino.h" @@ -32,6 +33,16 @@ #include "root-dev-ino.h" #include "xfts.h"

+/* Some systems only have <sys/vfs.h>, other systems also

have <sys/statfs.h>, where the former includes the latter.
So it seems including the former is the best choice. */ +#include "fs.h" +#if HAVE_SYS_VFS_H +# include <sys/vfs.h> +#else +# include <sys/statfs.h> +#endif
/* The official name of this program (e.g., no `g' prefix). */ #define PROGRAM_NAME "chmod"

@@ -83,6 +94,9 @@ static enum Verbosity verbosity = V_off; Otherwise NULL. */ static struct dev_ino *root_dev_ino;

+/* The effective user ID of the caller process. / +static uid_t euid; + / For long options that have no equivalent short option, use a non-character as a pseudo short option, starting with CHAR_MAX + 1. */ enum @@ -170,6 +184,42 @@ describe_change (const char *file, mode_t mode, (unsigned long int) (mode & CHMOD_MODE_BITS), &perms[1]); }

+/* Return true if the file resides on NFS filesystem.

Limit this optimization to systems that provide fstatfs. */
+#if HAVE_FSTATFS && HAVE_SYS_STATFS_H && HAVE_STRUCT_STATFS_F_TYPE

+static bool +may_have_nfsacl (FTSENT const *ent) +{

int fd;
int cwd_fd = ent->fts_fts->fts_cwd_fd;
char const *file = ent->fts_accpath;
struct statfs buf;
fd = openat (cwd_fd, file, O_RDONLY);
if (0 <= fd)
{

 /* If fstatfs fails, assume we can't use the optimization.  */

```
 if (fstatfs (fd, &buf) < 0)
```
```
   {
```
```
     close (fd);
```
```
     return true;
```
```
  }
```
```
 close (fd);
```
```
 return buf.f_type == S_MAGIC_NFS;
```
}
char const *file_full_name = ent->fts_path;
if (statfs (file_full_name, &buf) < 0)
return true;
return buf.f_type == S_MAGIC_NFS; +} +#else +# define may_have_nfsacl(ignored) (true) +#endif
/* Change the mode of FILE. Return true if successful. This function is called once for every file system object that fts encounters. */ @@ -258,16 +308,38 @@ process_file (FTS *fts, FTSENT *ent) new_mode = mode_adjust (old_mode, S_ISDIR (old_mode) != 0, umask_value, change, NULL);

```
 if (! S_ISLNK (old_mode))
```

 /* Do not touch the inode if the new file mode is the same as it was

before;

    This is an optimization for some cases. However, the new behavior

must be

    disabled for filesystems that support NFSv4 ACLs.

    This idea suggest by Paul Eggert refer to FreeBSD chmod(1).

    It uses pathconf(2)/lpathconf(2) to determine whether this is the

case.

    But we lack of them on linux, Instead, calling fstatfs(2) and compare

the

    f_type we can still do optimization at least its not NFS.  */

 if ((old_mode & CHMOD_MODE_BITS) == new_mode)
   {

     if (chmodat (fts->fts_cwd_fd, file, new_mode) == 0)

```
       chmod_succeeded = true;
```
```
     else
```

     if (!may_have_nfsacl (ent))
       {

```
         if (! force_silent)
```

           error (0, errno, _("changing permissions of %s"),

         if (file_stats->st_uid != euid && euid != 0)

           error (0, EPERM, _("changing permission of %s"),
                  quote (file_full_name));

```
         ok = false;
```

```
         else
```
```
           chmod_succeeded = true;
```
```
       }
```
```
  }
```
```
 else
```
```
   {
```
```
     if (! S_ISLNK (old_mode))
```
```
       {
```

         if (chmodat (fts->fts_cwd_fd, file, new_mode) == 0)

```
           chmod_succeeded = true;
```
```
         else
```
```
           {
```
```
             if (! force_silent)
```

               error (0, errno, _("changing permissions of %s"),

                      quote (file_full_name));

```
             ok = false;
```
```
           }
       }
   }
```
} @@ -545,6 +617,7 @@ main (int argc, char **argv) root_dev_ino = NULL; }
euid = geteuid (); ok = process_files (argv + optind, FTS_COMFOLLOW | FTS_PHYSICAL | FTS_DEFER_STAT);

-- 1.5.4.3

Re: modify chmod, (continued)
* Re: modify chmod, jeff.liu, 2010/02/05
* Re: modify chmod, Eric Blake, 2010/02/05
* Re: modify chmod, jeff.liu, 2010/02/05
* Re: modify chmod, jeff.liu, 2010/02/06
* Re: modify chmod, jeff.liu, 2010/02/06
* Re: modify chmod, Jim Meyering, 2010/02/06
* Re: modify chmod, jeff.liu, 2010/02/07
* Re: modify chmod, Jim Meyering, 2010/02/07
* Re: modify chmod, jeff.liu, 2010/02/07
* Re: modify chmod, Jim Meyering, 2010/02/07
* Re: modify chmod,jeff.liu <=
* Re: modify chmod, jeff.liu, 2010/02/08
* Re: modify chmod, Jim Meyering, 2010/02/13
* Re: modify chmod, jeff.liu, 2010/02/21
* Re: modify chmod, Jim Meyering, 2010/02/21
* Message not available
* Re: modify chmod, Jim Meyering, 2010/02/21
* Re: modify chmod, jeff.liu, 2010/02/21
- Re: modify chmod, jeff.liu, 2010/02/05

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