Re: Linux 2.4.20-pre4-ac2

[Christoph Hellwig <hch@infradead.org>]

On Mon, Aug 26, 2002 at 06:35:04AM -0400, Alan Cox wrote:
> o	Khttpd race fixes				(Dan Kegel)

This includes some wrong documentation updates:

+   kHTTPd is *not* currently compatible with tmpfs.  Trying to serve
+   files stored on a tmpfs partition is known to cause kernel oopses
+   as of 2.4.18.  This is due to the same problem that prevents sendfile()
+   from being usable with tmpfs.  A tmpfs patch is floating around that seems
+   to fix this, but has not been released as of 27 May 2002.
+   kHTTPD does work fine with ramfs, though.

This is _not_ a problem with tmpfs, but with khttpd.  The same problem
is also present with nay filesystem that uses the pagecache but not
generic_file_read or a non-trivial wrapper around generic_file_read, such
as smbfs, ncpff, nfs, (open-)gfs, or xfs.  This might not always mean
those filesystems don't work at all with khttpd, but at least it opens
race conditions.  khttpd uses do_generic_file_read directly instead of
using a file operation, and the problem is that do_generic_file_read
should never have been exported to allow such a layering violation.
sendfile() and the loop driver have the same issue. In 2.5 of those
only the loop issue is still existant, and I plan to fix that one and
make do_generic_file_read static.

+   There is debate about whether to remove kHTTPd from the main
+   kernel sources.  This will probably happen in the 2.5 kernel series,
+   after which khttpd will still be available as a patch.

khttpd is gone in 2.5