On 2020/06/18 22:11, Sungjong Seo wrote:
BTW
Even with this patch applied, VOL_DIRTY remains until synced in the above
case.
It's not easy to reproduce as rmdir, but I'll try to fix it in the future.
I think it's not a problem not to clear VOL_DIRTY under real errors,
because VOL_DIRTY is just like a hint to note that write was not finished clearly.
If you mean there are more situation like ENOTEMPTY you mentioned,
please make new patch to fix them.
When should VOL_DIRTY be cleared?
The current behavior is ...
Case of mkdir, rmdir, rename:
- set VOL_DIRTY before operation
- set VOL_CLEAN after operating.
In async mode, it is actually written to the media after 30 seconds.
Case of cp, touch:
- set VOL_DIRTY before operation
- however, VOL_CLEAN is not called in this context.
VOL_CLEAN will call by sync_fs or unmount.
I added VOL_CLEAN in last of __exfat_write_inode() and exfat_map_cluster().
As a result, VOL_DIRTY is cleared with cp and touch.
However, when copying a many files ...
- Async mode: VOL_DIRTY is written to the media twice every 30 seconds.
- Sync mode: Of course, VOL_DIRTY and VOL_CLEAN to the media for each file.
Frequent writing VOL_DIRTY and VOL_CLEAN increases the risk of boot-sector curruption.
If the boot-sector corrupted, it causes the following serious problems on some OSs.
- misjudge as unformatted
- can't judge as exfat
- can't repair
I want to minimize boot sector writes, to reduce these risk.
I looked vfat/udf implementation, which manages similar dirty information on linux,
and found that they ware mark-dirty at mount and cleared at unmount.
Here are some ways to clear VOL_DIRTY.
(A) VOL_CLEAN after every write operation.
:-) Ejectable at any time after a write operation.
:-( Many times write to Boot-sector.
(B) dirty at mount, clear at unmount (same as vfat/udf)
:-) Write to boot-sector twice.
:-( It remains dirty unless unmounted.
:-( Write to boot-sector even if there is no write operation.
(C) dirty on first write operation, clear on unmount
:-) Writing to boot-sector is minimal.
:-) Will not write to the boot-sector if there is no write operation.
:-( It remains dirty unless unmounted.
(D) dirty on first write operation, clear on sync-fs/unmount
:-) Writing to boot-sector can be reduced.
:-) Will not write to the boot-sector if there is no write operation.
:-) sync-fs makes it clean and ejectable immidiately.
:-( It remains dirty unless sync-fs or unmount.
:-( Frequent sync-fs will increases writes to boot-sector.
I think it should be (C) or(D).
What do you think?
BR
---
Tetsuhiro Kohada <kohada.t2@xxxxxxxxx>
