[PATCH] fat: Add nobarrier to workaround the strange behavior of device

OGAWA Hirofumi
2019-06-28T14:26:54Z

There was the report of strange behavior of device with recent
blkdev_issue_flush() position change.

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.

Cc: <stable@vger.kernel.org>
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
---

fs/fat/fat.h | 1 +
fs/fat/file.c | 8 ++++++--
fs/fat/inode.c | 16 ++++++++++++++--
3 files changed, 21 insertions(+), 4 deletions(-)

diff -puN fs/fat/fat.h~fat-nobarrier fs/fat/fat.h
--- linux/fs/fat/fat.h~fat-nobarrier 2019-06-28 21:22:18.146191739 +0900
+++ linux-hirofumi/fs/fat/fat.h 2019-06-28 21:59:11.693934616 +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 */
};

diff -puN fs/fat/file.c~fat-nobarrier fs/fat/file.c
--- linux/fs/fat/file.c~fat-nobarrier 2019-06-28 21:22:18.147191734 +0900
+++ linux-hirofumi/fs/fat/file.c 2019-06-28 21:59:11.693934616 +0900
@@ -193,17 +193,21 @@ static int fat_file_release(struct inode
int fat_file_fsync(struct file *filp, loff_t start, loff_t end, int datasync)
{
struct inode *inode = filp->f_mapping->host;
+ struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
int err;

err = __generic_file_fsync(filp, start, end, datasync);
if (err)
return err;

- err = sync_mapping_buffers(MSDOS_SB(inode->i_sb)->fat_inode->i_mapping);
+ err = sync_mapping_buffers(sbi->fat_inode->i_mapping);
if (err)
return err;

- return blkdev_issue_flush(inode->i_sb->s_bdev, GFP_KERNEL, NULL);
+ if (sbi->options.barrier)
+ err = blkdev_issue_flush(inode->i_sb->s_bdev, GFP_KERNEL, NULL);
+
+ return err;
}

diff -puN fs/fat/inode.c~fat-nobarrier fs/fat/inode.c
--- linux/fs/fat/inode.c~fat-nobarrier 2019-06-28 21:22:18.148191730 +0900
+++ linux-hirofumi/fs/fat/inode.c 2019-06-28 21:59:11.694934611 +0900
@@ -1016,6 +1016,8 @@ static int fat_show_options(struct seq_f
seq_puts(m, ",nfs=stale_rw");
if (opts->discard)
seq_puts(m, ",discard");
+ if (!opts->barrier)
+ seq_puts(m, ",nobarrier");
if (opts->dos1xfloppy)
seq_puts(m, ",dos1xfloppy");

@@ -1031,8 +1033,9 @@ enum {
Opt_shortname_winnt, Opt_shortname_mixed, Opt_utf8_no, Opt_utf8_yes,
Opt_uni_xl_no, Opt_uni_xl_yes, Opt_nonumtail_no, Opt_nonumtail_yes,
Opt_obsolete, Opt_flush, Opt_tz_utc, Opt_rodir, Opt_err_cont,
- Opt_err_panic, Opt_err_ro, Opt_discard, Opt_nfs, Opt_time_offset,
- Opt_nfs_stale_rw, Opt_nfs_nostale_ro, Opt_err, Opt_dos1xfloppy,
+ Opt_err_panic, Opt_err_ro, Opt_discard, Opt_barrier, Opt_nobarrier,
+ Opt_nfs, Opt_time_offset, Opt_nfs_stale_rw, Opt_nfs_nostale_ro,
+ Opt_err, Opt_dos1xfloppy,
};

static const match_table_t fat_tokens = {
@@ -1062,6 +1065,8 @@ static const match_table_t fat_tokens =
{Opt_err_panic, "errors=panic"},
{Opt_err_ro, "errors=remount-ro"},
{Opt_discard, "discard"},
+ {Opt_barrier, "barrier"},
+ {Opt_nobarrier, "nobarrier"},
{Opt_nfs_stale_rw, "nfs"},
{Opt_nfs_stale_rw, "nfs=stale_rw"},
{Opt_nfs_nostale_ro, "nfs=nostale_ro"},
@@ -1146,6 +1151,7 @@ static int parse_options(struct super_bl
opts->numtail = 1;
opts->usefree = opts->nocase = 0;
opts->tz_set = 0;
+ opts->barrier = 1;
opts->nfs = 0;
opts->errors = FAT_ERRORS_RO;
*debug = 0;
@@ -1335,6 +1341,12 @@ static int parse_options(struct super_bl
case Opt_discard:
opts->discard = 1;
break;
+ case Opt_barrier:
+ opts->barrier = 1;
+ break;
+ case Opt_nobarrier:
+ opts->barrier = 0;
+ break;

/* obsolete mount options */
case Opt_obsolete:
_