Re: modify chmod (original) (raw)

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From: jeff.liu
Subject: Re: modify chmod
Date: Mon, 08 Feb 2010 22:53:35 +0800
User-agent: Thunderbird 2.0.0.14 (X11/20080505)

jeff.liu 写道:

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 also tried to pass over the openat(), instead just comparing the fts_cwd_fd againt AT_FDCWD, if the pathname is interpreted relative to the current working directory of the calling process, call statfs(). or call fstafs(fts_cwd_fd...).

But consider the bind-mounted directory, it is not a proper way. Anyway, I add a timer instruments to help figure out the performance difference between may_have_acl() and chmodat(), If does not have to call openat(), the performance looks fine.

Please check the following test results: address@hidden:~/opensource_dev/coreutils$ time yes | sudo ./src/chmod -R 755 /ocfs2/ Time spent: 1.419816

real 0m10.584s user 0m0.296s sys 0m10.045s address@hidden:~/opensource_dev/coreutils$ time yes | sudo ./src/chmod -R 755 /ocfs2/ Time spent: 1.256965

real 0m9.176s user 0m0.220s sys 0m8.841s address@hidden:~/opensource_dev/coreutils$ time yes | sudo ./src/chmod -R 644 /ocfs2/ Time spent: 9.245956

real 0m17.541s user 0m0.344s sys 0m17.053s address@hidden:~/opensource_dev/coreutils$ time yes | sudo ./src/chmod -R 644 /ocfs2/ Time spent: 1.494338

real 0m10.972s user 0m0.360s sys 0m10.293s

code diff based on the last replay:

diff --git a/src/chmod.c b/src/chmod.c index b49adb8..430ee6f 100644 --- a/src/chmod.c +++ b/src/chmod.c @@ -21,6 +21,7 @@ #include <getopt.h> #include <sys/types.h> #include <unistd.h> +#include <sys/time.h>

#include "system.h" #include "dev-ino.h" @@ -194,8 +195,10 @@ may_have_nfsacl (FTSENT const *ent) int fd; int cwd_fd = ent->fts_fts->fts_cwd_fd; char const *file = ent->fts_accpath;

+#if 0 fd = openat (cwd_fd, file, O_RDONLY); if (0 <= fd) { @@ -209,10 +212,18 @@ may_have_nfsacl (FTSENT const *ent) close (fd); return buf.f_type == S_MAGIC_NFS; } +#endif

return buf.f_type == S_MAGIC_NFS; } @@ -220,6 +231,8 @@ may_have_nfsacl (FTSENT const *ent)

define may_have_nfsacl(ignored) (true)

#endif

+double tot_timer_spent; + /* Change the mode of FILE. Return true if successful. This function is called once for every file system object that fts encounters. */ @@ -234,6 +247,9 @@ process_file (FTS *fts, FTSENT *ent) mode_t new_mode IF_LINT (= 0); bool ok = true; bool chmod_succeeded = false;

@@ -318,6 +334,8 @@ process_file (FTS *fts, FTSENT *ent)

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

@@ -326,11 +344,18 @@ process_file (FTS *fts, FTSENT *ent) else chmod_succeeded = true; } +

1000000.0);

@@ -340,6 +365,11 @@ process_file (FTS *fts, FTSENT *ent) quote (file_full_name)); ok = false; } +

1000000.0);