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authorAlan Jenkins <alan-jenkins@tuffmail.co.uk>2008-07-27 04:38:42 -0400
committerJames Bottomley <James.Bottomley@HansenPartnership.com>2008-07-27 10:16:13 -0400
commit2b142900784c6e38c8d39fa57d5f95ef08e735d8 (patch)
treee7d51b58df76e864c91ff7ffca0229027328c588 /drivers
parent4cfc51017db3e3f4eaaa2cb436a905097a4f08e2 (diff)
[SCSI] extend the last_sector_bug flag to cover more sectors
The last_sector_bug flag was added to work around a bug in certain usb cardreaders, where they would crash if a multiple sector read included the last sector. The original implementation avoids this by e.g. splitting an 8 sector read which includes the last sector into a 7 sector read, and a single sector read for the last sector. The flag is enabled for all USB devices. This revealed a second bug in other usb cardreaders, which crash when they get a multiple sector read which stops 1 sector short of the last sector. Affected hardware includes the Kingston "MobileLite" external USB cardreader and the internal USB cardreader on the Asus EeePC. Extend the last_sector_bug workaround to ensure that any access which touches the last 8 hardware sectors of the device is a single sector long. Requests are shrunk as necessary to meet this constraint. This gives us a safety margin against potential unknown or future bugs affecting multi-sector access to the end of the device. The two known bugs only affect the last 2 sectors. However, they suggest that these devices are prone to fencepost errors and that multi-sector access to the end of the device is not well tested. Popular OS's use multi-sector accesses, but they rarely read the last few sectors. Linux (with udev & vol_id) automatically reads sectors from the end of the device on insertion. It is assumed that single sector accesses are more thoroughly tested during development. Signed-off-by: Alan Jenkins <alan-jenkins@tuffmail.co.uk> Tested-by: Alan Jenkins <alan-jenkins@tuffmail.co.uk> Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/scsi/sd.c21
-rw-r--r--drivers/scsi/sd.h6
2 files changed, 21 insertions, 6 deletions
diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 8e08d51a0f05..e5e7d7856454 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -375,6 +375,7 @@ static int sd_prep_fn(struct request_queue *q, struct request *rq)
375 struct gendisk *disk = rq->rq_disk; 375 struct gendisk *disk = rq->rq_disk;
376 struct scsi_disk *sdkp; 376 struct scsi_disk *sdkp;
377 sector_t block = rq->sector; 377 sector_t block = rq->sector;
378 sector_t threshold;
378 unsigned int this_count = rq->nr_sectors; 379 unsigned int this_count = rq->nr_sectors;
379 unsigned int timeout = sdp->timeout; 380 unsigned int timeout = sdp->timeout;
380 int ret; 381 int ret;
@@ -422,13 +423,21 @@ static int sd_prep_fn(struct request_queue *q, struct request *rq)
422 } 423 }
423 424
424 /* 425 /*
425 * Some devices (some sdcards for one) don't like it if the 426 * Some SD card readers can't handle multi-sector accesses which touch
426 * last sector gets read in a larger then 1 sector read. 427 * the last one or two hardware sectors. Split accesses as needed.
427 */ 428 */
428 if (unlikely(sdp->last_sector_bug && 429 threshold = get_capacity(disk) - SD_LAST_BUGGY_SECTORS *
429 rq->nr_sectors > sdp->sector_size / 512 && 430 (sdp->sector_size / 512);
430 block + this_count == get_capacity(disk))) 431
431 this_count -= sdp->sector_size / 512; 432 if (unlikely(sdp->last_sector_bug && block + this_count > threshold)) {
433 if (block < threshold) {
434 /* Access up to the threshold but not beyond */
435 this_count = threshold - block;
436 } else {
437 /* Access only a single hardware sector */
438 this_count = sdp->sector_size / 512;
439 }
440 }
432 441
433 SCSI_LOG_HLQUEUE(2, scmd_printk(KERN_INFO, SCpnt, "block=%llu\n", 442 SCSI_LOG_HLQUEUE(2, scmd_printk(KERN_INFO, SCpnt, "block=%llu\n",
434 (unsigned long long)block)); 443 (unsigned long long)block));
diff --git a/drivers/scsi/sd.h b/drivers/scsi/sd.h
index 550b2f70a1f8..95b9f06534d5 100644
--- a/drivers/scsi/sd.h
+++ b/drivers/scsi/sd.h
@@ -31,6 +31,12 @@
31 */ 31 */
32#define SD_BUF_SIZE 512 32#define SD_BUF_SIZE 512
33 33
34/*
35 * Number of sectors at the end of the device to avoid multi-sector
36 * accesses to in the case of last_sector_bug
37 */
38#define SD_LAST_BUGGY_SECTORS 8
39
34struct scsi_disk { 40struct scsi_disk {
35 struct scsi_driver *driver; /* always &sd_template */ 41 struct scsi_driver *driver; /* always &sd_template */
36 struct scsi_device *device; 42 struct scsi_device *device;