Messages in this thread | | | Date | Wed, 4 Nov 2009 15:22:34 -0500 | From | Jeff Layton <> | Subject | Re: make getdents/readdir POSIX compliant wrt mount-point dirent.d_ino |
| |
On Thu, 3 Sep 2009 14:50:52 +0000 (UTC) Eric Blake <ebb9@byu.net> wrote:
> Ulrich Drepper <drepper <at> gmail.com> writes: > > > I guess that this is really a difficult way to solve. I wouldn't want > > to pay for something which is hardly ever really used. > > > > But there are programs out there which would like to use the inode > > uniqueness. Therefore the next best thing to do is perhaps to return > > a flag in the getdents information (in d_type, perhaps) to indicate > > that this is a mount point and/or that there are multiple ways to > > access the file in question. Then programs which can use the inode > > information can be watching for this flag and enter the slow path only > > if it's set. > > An alternative to a flag in d_type might be setting d_ino to a sentinel value > (there is plenty of existing code that refuses to use a readdir entry with d_ino > of 0, so it would have to be something else; but maybe -1 would work). But I > definitely like your idea of making it obvious to the application (whether by > d_ino or d_type) when it is necessary to use lstat to validate the inode number, > and promising that if the flag is not set then d_ino is correct. >
The only problem with those schemes is that they assume that you're using getdents. If you just lstat something then it's not clear.
It seems like a better scheme might be to do something that makes this clear when using an lstat call too. Maybe we could coopt a bit in the st_mode?
S_IFXDEV 020000
That's outside of the S_IFMT mask, so it shouldn't break S_IS* checks, right?
-- Jeff Layton <jlayton@redhat.com>
| |