[PATCH] Fix hanging close for /dev/mtd
joakim.tjernlund at transmode.se
Wed Jun 13 13:16:31 EDT 2007
On Wed, 2007-06-13 at 16:29 +0200, Jörn Engel wrote:
> [ Putting David on Cc:. This is a bug report for JFFS2 ]
> On Wed, 13 June 2007 15:29:38 +0200, Joakim Tjernlund wrote:
> > On Wed, 2007-06-13 at 13:54 +0200, Jörn Engel wrote:
> > >
> > > In this case you made me wonder. What is the mtd->sync method supposed
> > > to accomplish anyway? mtd->write is synchronous, mtd->erase de-facto
> > > also is. So it cannot be a sync in the sense of "flush all dirty data
> > > to flash and don't return before you're finished". Or can it?
> > Yes, this is also my view(for NOR flash, NAND is diffrent).
> > mtd->erase can be suspended though, but it doesn't matter
> > in this case. However, I don't know enough to be 100% sure
> At the very least that method needs better documentation than:
> /* Sync */
> void (*sync) (struct mtd_info *mtd);
> I can see two sane alternatives.
> * An MTD driver may return from mtd->write() calls before the data has
> * safely been written to the medium. Any amount of dirty data may be
> * cached by either the driver or the device. If a filesystem depends
> * on the data being safely on the medium, it has to explicitly call
> * mtd->sync().
> * Mtd->write() and mtd->erase() methods may only return if the data has
> * been safely written to the device. Special care needs to be taken
> * for devices that support caching.
> My tendency is to favor the first variant.
> Block2mtd already implements
> it. And if we went for variant two, mtd->sync() would be pointless and
> should get removed.
> Now to the bug report:
> JFFS2 must call mtd->sync() for its various sync routines. If mounted
> with -o sync or for files opened with O_SYNC, it has to call that after
> every write. If nothing else, it is currently broken on block2mtd.
Sure, but for NOR flash this sync can be a NOP, right?
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