On Fri, 28 Jun 2019 23:32:06 +0900 OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx> wrote:
>
> v2:
> Just cleanup, changed the place of options under comment of fat.
>
> ---
Please be careful with the "^---$" - it denotes "end of changelog", so
I ended up without a changelog!
> There was the report of strange behavior of device with recent
> blkdev_issue_flush() position change.
A Reported-by: would be nice, but not necessary.
> The following is simplified usbmon trace.
>
> 4203 9.160230 host -> 1.25.1 USBMS 95 SCSI: Synchronize Cache(10) LUN: 0x00 (LBA: 0x00000000, Len: 0)
> 4206 9.164911 1.25.1 -> host USBMS 77 SCSI: Response LUN: 0x00 (Synchronize Cache(10)) (Good)
> 4207 9.323927 host -> 1.25.1 USBMS 95 SCSI: Read(10) LUN: 0x00 (LBA: 0x00279950, Len: 240)
> 4212 9.327138 1.25.1 -> host USBMS 77 SCSI: Response LUN: 0x00 (Read(10)) (Good)
>
> [...]
>
> 7323 10.202167 host -> 1.25.1 USBMS 95 SCSI: Synchronize Cache(10) LUN: 0x00 (LBA: 0x00000000, Len: 0)
> 7326 10.432266 1.25.1 -> host USBMS 77 SCSI: Response LUN: 0x00 (Synchronize Cache(10)) (Good)
> 7327 10.769092 host -> 1.25.1 USBMS 95 SCSI: Test Unit Ready LUN: 0x00
> 7330 10.769192 1.25.1 -> host USBMS 77 SCSI: Response LUN: 0x00 (Test Unit Ready) (Good)
> 7335 12.849093 host -> 1.25.1 USBMS 95 SCSI: Test Unit Ready LUN: 0x00
> 7338 12.849206 1.25.1 -> host USBMS 77 SCSI: Response LUN: 0x00 (Test Unit Ready) (Check Condition)
> 7339 12.849209 host -> 1.25.1 USBMS 95 SCSI: Request Sense LUN: 0x00
>
> If "Synchronize Cache" command issued then there is idle time, the
> device stop to process further commands, and behave as like no media.
> (it returns NOT_READY [MEDIUM NOT PRESENT] for SENSE command, and this
> happened on Kindle) [just a guess, the device is trying to detect the
> "safe-unplug" operation of Windows or such?]
>
> To workaround those devices and provide flexibility, this adds
> "barrier"/"nobarrier" mount options to fat driver.
I think it would be helpful if the changelog were to at least describe
the longer-term plan which hch described.
> --- linux/fs/fat/fat.h~fat-nobarrier 2019-06-28 21:22:18.146191739 +0900
> +++ linux-hirofumi/fs/fat/fat.h 2019-06-28 23:26:04.881215721 +0900
> @@ -51,6 +51,7 @@ struct fat_mount_options {
> tz_set:1, /* Filesystem timestamps' offset set */
> rodir:1, /* allow ATTR_RO for directory */
> discard:1, /* Issue discard requests on deletions */
> + barrier:1, /* Issue FLUSH command */
> dos1xfloppy:1; /* Assume default BPB for DOS 1.x floppies */
Documentation/filesystems/vfat.txt should be updated to describe this
new option please. And perhaps to mention that a device-level quirk should be
used in preference, if it is available.
