named pipe writes on readonly filesystems

[Chris Mason <mason@suse.com>]

Hello everyone,

Since fs/pipe.c:pipe_write() calls mark_inode_dirty, and it is legal to
write to a named pipe on a readonly filesystem, we can end up writing an
inode on a readonly FS.

reiserfs prints a warning whenever someone tries to write an inode on a
readonly FS, so we've been getting a few complaints about this.

I see at least 3 choices:

drop the reiserfs warning, it was only there to chase things similar to the
remount root readonly bug in 2.4.0.

change mark_inode_dirty or write_inode to exit early on readonly
filesystems.

change pipe_write to leave the inode clean when the FS is readonly.

Does anyone have a preference?  I'd rather not see each FS have to check
for this on their own, but the other filesystems aren't as picky as
reiserfs in this case ;-)

-chris