Re: modify chmod (original) (raw)

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From: Jim Meyering
Subject: Re: modify chmod
Date: Sun, 07 Feb 2010 14:15:03 +0100

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 >> +mayhavenfsacl(const char *file) >> +{ >> +# if HAVESYSVFSH && HAVESYSSTATFSH && HAVESTRUCTSTATFSFTYPE >> + 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. 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.