Messages in this thread | | | Date | Tue, 23 Nov 2004 21:35:52 -0800 | From | Matt Mackall <> | Subject | Re: [PATCH] let fat handle MS_SYNCHRONOUS flag |
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On Wed, Nov 24, 2004 at 02:00:54PM +0900, OGAWA Hirofumi wrote: > Matt Mackall <mpm@selenic.com> writes: > > > On Wed, Nov 24, 2004 at 05:24:36AM +0900, OGAWA Hirofumi wrote: > >> Colin Leroy <colin@colino.net> writes: > >> > >> > It adds MS_SYNCHRONOUS support to FAT filesystem, so that less > >> > filesystem breakage happen when disconnecting an USB key, for > >> > example. I'd like to have comments about it, because as it > >> > seems to work fine here, I'm not used to fs drivers and could > >> > have made mistakes. > >> > >> What cases should these patches guarantee that users can unplug the > >> USB key? And can we guarantee the same cases by improving autofs or > >> the similar stuff? > > > > Well there can be no guarantees - there will always be a race between > > flush and hot unplug. If we're careful with write ordering, we can > > perhaps arrange to avoid the worst sorts of corruption, provided the > > device does the right thing when it's in the middle of an IO. > > > > But generally I think this is a good idea as it shrinks the window. > > Things which I want to say here - do we really need the bogus > sync-mode?
I'm not sure why you say it's bogus. Ext2 for instance has long had a mount option similar to this and it makes sense in volatile environments. Having the flag in the superblock seems a sensible way of doing it as well.
> Current fatfs is not keeping the consistency of data on the disk at > all. So, after all, the data on a disk is corrupting until all > syscalls finish, right?
This is to protect against usage patters like mv a b, oh look, it's done, unplug. Not lots of active readers/writers.
> If so, isn't this too slow? I doubt this is good solution for this > problem (USB key unplugging)...
Perhaps. I think the behavior should be to honor the superblock flag by default, overridable with -o sync|async at mount. > Well, it seems good as start of sync-mode though. > -- > OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
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