FAT/VFAT and the sync flag

FAT/VFAT and the sync flag

[Scott Bronson]

Can anyone tell me if the VFAT filesystem actually recognizes the sync
flag?  Early in 2.4, it appeared that it was ignoring it.

However, now that a lot of USB devices are VFAT, this gets pretty
important.

Thanks,

    - Scott

Re: FAT/VFAT and the sync flag

[Randy.Dunlap]

On 3 Oct 2002, Scott Bronson wrote:

| Can anyone tell me if the VFAT filesystem actually recognizes the sync
| flag?  Early in 2.4, it appeared that it was ignoring it.
|
| However, now that a lot of USB devices are VFAT, this gets pretty
| important.
| -

USB devices (mostly) don't care what filesystem is on them.
I have used ext2 on USB floppies and USB Zip.
You should be able to put any supported filesystem on them.
The only case I know of that matters is MP3 players, which
do expect/require a VFAT filesystem (it's usually all they know),
so media that is used in MP3 players should be VFAT probably. :)

Now, for you first question, I hope that Ogawa or Al or Christoph
et al can answer it, but my guess is, No, VFAT doesn't
recognize the sync flag.  I base that on grepping for
s_sync and for MS_SYNCHRONOUS in linux/fs/{fat,vfat,msdos}
and finding s_sync a few times, but not finding MS_SYNCHRONOUS
at all.

'man mount' says that the sync flag is only honored by
ext2, ext3, and ufs.
I see it checked/used in ext2, ufs, and ntfs.

-- 
~Randy

Re: FAT/VFAT and the sync flag

[OGAWA Hirofumi]

"Randy.Dunlap" <rddunlap@osdl.org> writes:

> On 3 Oct 2002, Scott Bronson wrote:
> 
> | Can anyone tell me if the VFAT filesystem actually recognizes the sync
> | flag?  Early in 2.4, it appeared that it was ignoring it.
> |
> | However, now that a lot of USB devices are VFAT, this gets pretty
> | important.
> 
> Now, for you first question, I hope that Ogawa or Al or Christoph
> et al can answer it, but my guess is, No, VFAT doesn't
> recognize the sync flag.  I base that on grepping for
> s_sync and for MS_SYNCHRONOUS in linux/fs/{fat,vfat,msdos}
> and finding s_sync a few times, but not finding MS_SYNCHRONOUS
> at all.

You are right. The fatfs just ignore the sync flag.
-- 
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>

Re: FAT/VFAT and the sync flag

[Scott Bronson]

On Fri, 2002-10-04 at 08:33, OGAWA Hirofumi wrote:
> You are right. The fatfs just ignore the sync flag.

"Randy.Dunlap" <rddunlap@osdl.org> writes:
> What advantage would implementing sync have for FAT-fs?
> When you unmount a device (before removing it), the filesystem
> is automatically sync-ed (with some possible delay time here to
> perform I/O).  That could provide a quicker unmount, at the
> expense of spreading the device (filesystem) I/O out across
> all device reads/writes over time.  (did that make sense?) ...
> Is there some usage scenario that you are interested in that I am
> just missing?

That made perfect sense.  However, I'm happy with the unmount times. 
I'm worried about ham-fisted users.

When you unplug a VFAT-mounted device from FireWire or USB without
remembering to unmount it first, you get instant file system
corruption.  I've done it a few times myself even though I know better! 
I'm in a hurry, I grab the device, poof!  It's now broken until I can
run fsck.vfat on it and restore missing files.  It's not fun.

If VFAT supported the sync flag, then neglecting to unmount it would not
be so catastrophic.  Well, unless you unplug it in the middle of disk
activity, in which case you're asking for it.  :)

I'd just like Linux to try to avoid dying catastrophically if someone
makes a simple mistake.  Any idea how much effort it would take to add
sync support to VFAT?  Thanks,

    - Scott