Date: Thu, 18 Nov 2004 14:45:40 +0100 From: Erik Trulsson <ertr1013@student.uu.se> To: Mikhail Teterin <Mikhail.Teterin@murex.com> Cc: freebsd-current@freebsd.org Subject: Re: open(), mmap(), sendfile() vs. the file's access time Message-ID: <20041118134539.GA26538@falcon.midgard.homeip.net> In-Reply-To: <200411171407.11793.Mikhail.Teterin@murex.com> References: <200411171407.11793.Mikhail.Teterin@murex.com>
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On Wed, Nov 17, 2004 at 02:07:11PM -0500, Mikhail Teterin wrote:
> Hello!
>
> It appears, only read() modifies a file's atime. Otherwise, a file can be
> open()-ed and subsequently _accessed_ through mmap or sendfile()-ed away
> without atime being changed. Does not seem right...
>
> Should open() update atime? My first reaction would be yes, but on Linux and
> Solaris the behaviour is the same (try attached program).
>
> Should sendfile()? What about mmap() -- there are some hairy usages?..
I don't know if the current behaviour is "right", but it is certainly
consistent with the documentation. From the manpage for stat(2):
The time-related fields of struct stat are as follows:
st_atime Time when file data last accessed. Changed by the
mknod(2), utimes(2) and read(2) system calls.
st_mtime Time when file data last modified. Changed by the
mknod(2), utimes(2) and write(2) system calls.
st_ctime Time when file status was last changed (inode data
modification). Changed by the chmod(2), chown(2),
link(2), mknod(2), rename(2), unlink(2), utimes(2) and
write(2) system calls.
The Solaris stat(2) manpage says:
st_atime
Time when file data was last accessed. Changed by the
following functions: creat(), mknod(), pipe(),
utime(2), and read(2).
st_mtime
Time when data was last modified. Changed by the fol-
lowing functions: creat(), mknod(), pipe(), utime(),
and write(2).
st_ctime
Time when file status was last changed. Changed by the
following functions: chmod(), chown(), creat(),
link(2), mknod(), pipe(), unlink(2), utime(), and
write().
And on Linux stat(2) says:
The field st_atime is changed by file accesses, e.g. by execve(2),
mknod(2), pipe(2), utime(2) and read(2) (of more than zero bytes).
Other routines, like mmap(2), may or may not update st_atime.
The field st_mtime is changed by file modifications, e.g. by
mknod(2), truncate(2), utime(2) and write(2) (of more than zero
bytes). Moreover, st_mtime of a directory is changed by the
creation or deletion of files in that directory. The st_mtime field
is not changed for changes in owner, group, hard link count, or
mode.
The field st_ctime is changed by writing or by setting inode
information (i.e., owner, group, link count, mode, etc.).
It seems that one should definitely not depend on atime being changed
by mmap() or sendfile().
--
<Insert your favourite quote here.>
Erik Trulsson
ertr1013@student.uu.se
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