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Subject2.4 bug: fifo-write causes diskwrites to read-only fs !
Hi all,

It turns out that Linux is updating inode timestamps of fifos (named
pipes) that are written to while residing on a read-only filesystem.
It is not only updating in-ram info, but it will issue *physical*
writes to the read-only fs on the disk !

I use a CompactFlash in an embedded application with a read-only root-fs
on it. There are several processes that communicate with each other
via fifos. This bug in Linux causes frequent writes to my CF and will
shorten it's lifetime enormously ..

I've posted a report on the "mysterious writes" before:
( )
(incorrectly) linking it to a possible bug in O_SYNC. Nothing came out
of it.

But now I've completely tracked down the bug (logging all diskaccesses
and seeing it undoubtly write in disksectors containing time-stamp
info of fifo's). Looking back it would have been easier to prove that
something is wrong: the modified time-stamps survive power-cycles.
This is not supposed to happen on a read-only fs.

I've tried reading the kernel source to find where the bug lives,
But I'm not too familiar with it. Anyone out there who can
pin it down ?

Rob van Nieuwkerk

- various 2.4 kernels including RH-2.4.20-13.9,
but also straight 2.4(ac) ones.
- CompactFlash (= IDE disk)
- Geode GX1 CPU (i586 compatible)
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