Re: modify chmod (original) (raw)

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From: jeff.liu
Subject: Re: modify chmod
Date: Sun, 07 Feb 2010 22:55:55 +0800
User-agent: Thunderbird 2.0.0.14 (X11/20080505)

Jim Meyering 写道:

jeff.liu wrote:

Jim Meyering 写道:

jeff.liu wrote:

A tiny patch, make chmod do not touch the inode if the new file permission mode is same as it was before.

...

+static bool +may_have_nfsacl(const char *file) +{ +# if HAVE_SYS_VFS_H && HAVE_SYS_STATFS_H && HAVE_STRUCT_STATFS_F_TYPE

  • struct statfs buf;
  • /* If statfs fails, assume we can't use the optimization. */
  • if (statfs (file, &buf) < 0)

This function should accept a file descriptor, not a file name, and should call fstatfs, not statfs.

Thanks for the correction. IMHO, to get a fd, then call fstatfs ranther than statfs here, is to ensure the same file object proceeding to operated on?

fts provides a file descriptor for every directory it processes, so you can use an "FTS_ENT const *ent" parameter instead. When it refers to a directory, use ent->fts_fts->fts_cwd_fd as the file descriptor. Otherwise, you will have to call statfs after all.

thanks for the point out. Actually, by consulting your primary comments for using fstatfs(2), I was also thought the only way is pass the fts_cwd_fd to it, then I started to study the fts_xxxx() series functions and added debugging instruments to check the fts_cwd_fd value againt a five-depth directory. but at that time, I found many -100(AT_FDCWD) printed out somehow. so I took it for granted to call statfs since it can save the time if do not need to check the fts_cwd_fd against AT_FDCWD frequently.

At first, I was thinking we could avoid statfs most of the time (i.e., change device only at a directory), but with bind-mounted regular files, the device can change at any time during a traversal.