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-rw-r--r--target/linux/generic/hack-4.19/550-loop-better-discard-for-block-devices.patch164
1 files changed, 164 insertions, 0 deletions
diff --git a/target/linux/generic/hack-4.19/550-loop-better-discard-for-block-devices.patch b/target/linux/generic/hack-4.19/550-loop-better-discard-for-block-devices.patch
new file mode 100644
index 0000000000..d6f0f3df0a
--- /dev/null
+++ b/target/linux/generic/hack-4.19/550-loop-better-discard-for-block-devices.patch
@@ -0,0 +1,164 @@
+From: Evan Green <evgreen@chromium.org>
+Subject: [PATCH v5 0/2] loop: Better discard for block devices
+Date: Mon, 6 May 2019 11:27:35 -0700
+Message-Id: <20190506182736.21064-2-evgreen@chromium.org>
+
+This series addresses some errors seen when using the loop
+device directly backed by a block device.
+
+The first change titled "loop: Better discard for block devices"
+plumbs out the correct error message, and the second change prevents
+the error from occurring in many cases.
+
+The errors look like this:
+[ 90.880875] print_req_error: I/O error, dev loop5, sector 0
+
+The errors occur when trying to do a discard or write zeroes operation
+on a loop device backed by a block device that does not support write zeroes.
+Firstly, the error itself is incorrectly reported as I/O error, but is
+actually EOPNOTSUPP. The first patch plumbs out EOPNOTSUPP to properly
+report the error.
+
+The second patch called "loop: Better discard support for block devices"
+prevents these errors from occurring by mirroring the zeroing capabilities
+of the underlying block device into the loop device.
+Before this change, discard was always reported as being supported, and
+the loop device simply turns around and does an fallocate operation on the
+backing device. After this change, backing block devices that do support
+zeroing will continue to work as before, and continue to get all the
+benefits of doing that. Backing devices that do not support zeroing will
+fail earlier, avoiding hitting the loop device at all and ultimately
+avoiding this error in the logs.
+
+I can also confirm that this fixes test block/003 in the blktests, when
+running blktests on a loop device backed by a block device.
+
+Signed-off-by: Evan Green <evgreen@chromium.org>
+Reviewed-by: Ming Lei <ming.lei@redhat.com>
+Reviewed-by: Bart Van Assche <bvanassche@acm.org>
+Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
+Reviewed-by: Gwendal Grignou <gwendal@chromium.org>
+Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
+---
+
+--- a/drivers/block/loop.c
++++ b/drivers/block/loop.c
+@@ -416,19 +416,14 @@ out_free_page:
+ return ret;
+ }
+
+-static int lo_discard(struct loop_device *lo, struct request *rq, loff_t pos)
++static int lo_discard(struct loop_device *lo, struct request *rq,
++ int mode, loff_t pos)
+ {
+- /*
+- * We use punch hole to reclaim the free space used by the
+- * image a.k.a. discard. However we do not support discard if
+- * encryption is enabled, because it may give an attacker
+- * useful information.
+- */
+ struct file *file = lo->lo_backing_file;
+- int mode = FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE;
++ struct request_queue *q = lo->lo_queue;
+ int ret;
+
+- if ((!file->f_op->fallocate) || lo->lo_encrypt_key_size) {
++ if (!blk_queue_discard(q)) {
+ ret = -EOPNOTSUPP;
+ goto out;
+ }
+@@ -457,7 +452,9 @@ static void lo_complete_rq(struct reques
+
+ if (!cmd->use_aio || cmd->ret < 0 || cmd->ret == blk_rq_bytes(rq) ||
+ req_op(rq) != REQ_OP_READ) {
+- if (cmd->ret < 0)
++ if (cmd->ret == -EOPNOTSUPP)
++ ret = BLK_STS_NOTSUPP;
++ else if (cmd->ret < 0)
+ ret = BLK_STS_IOERR;
+ goto end_io;
+ }
+@@ -597,8 +594,13 @@ static int do_req_filebacked(struct loop
+ case REQ_OP_FLUSH:
+ return lo_req_flush(lo, rq);
+ case REQ_OP_DISCARD:
++ return lo_discard(lo, rq,
++ FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, pos);
++
+ case REQ_OP_WRITE_ZEROES:
+- return lo_discard(lo, rq, pos);
++ return lo_discard(lo, rq,
++ FALLOC_FL_ZERO_RANGE | FALLOC_FL_KEEP_SIZE, pos);
++
+ case REQ_OP_WRITE:
+ if (lo->transfer)
+ return lo_write_transfer(lo, rq, pos);
+@@ -853,6 +855,21 @@ static void loop_config_discard(struct l
+ struct file *file = lo->lo_backing_file;
+ struct inode *inode = file->f_mapping->host;
+ struct request_queue *q = lo->lo_queue;
++ struct request_queue *backingq;
++
++ /*
++ * If the backing device is a block device, mirror its zeroing
++ * capability. REQ_OP_DISCARD translates to a zero-out even when backed
++ * by block devices to keep consistent behavior with file-backed loop
++ * devices.
++ */
++ if (S_ISBLK(inode->i_mode) && !lo->lo_encrypt_key_size) {
++ backingq = bdev_get_queue(inode->i_bdev);
++ blk_queue_max_discard_sectors(q,
++ backingq->limits.max_write_zeroes_sectors);
++
++ blk_queue_max_write_zeroes_sectors(q,
++ backingq->limits.max_write_zeroes_sectors);
+
+ /*
+ * We use punch hole to reclaim the free space used by the
+@@ -860,22 +877,24 @@ static void loop_config_discard(struct l
+ * encryption is enabled, because it may give an attacker
+ * useful information.
+ */
+- if ((!file->f_op->fallocate) ||
+- lo->lo_encrypt_key_size) {
++ } else if ((!file->f_op->fallocate) || lo->lo_encrypt_key_size) {
+ q->limits.discard_granularity = 0;
+ q->limits.discard_alignment = 0;
+ blk_queue_max_discard_sectors(q, 0);
+ blk_queue_max_write_zeroes_sectors(q, 0);
+- blk_queue_flag_clear(QUEUE_FLAG_DISCARD, q);
+- return;
+- }
+
+- q->limits.discard_granularity = inode->i_sb->s_blocksize;
+- q->limits.discard_alignment = 0;
++ } else {
++ q->limits.discard_granularity = inode->i_sb->s_blocksize;
++ q->limits.discard_alignment = 0;
+
+- blk_queue_max_discard_sectors(q, UINT_MAX >> 9);
+- blk_queue_max_write_zeroes_sectors(q, UINT_MAX >> 9);
+- blk_queue_flag_set(QUEUE_FLAG_DISCARD, q);
++ blk_queue_max_discard_sectors(q, UINT_MAX >> 9);
++ blk_queue_max_write_zeroes_sectors(q, UINT_MAX >> 9);
++ }
++
++ if (q->limits.max_write_zeroes_sectors)
++ blk_queue_flag_set(QUEUE_FLAG_DISCARD, q);
++ else
++ blk_queue_flag_clear(QUEUE_FLAG_DISCARD, q);
+ }
+
+ static void loop_unprepare_queue(struct loop_device *lo)
+@@ -1893,7 +1912,10 @@ static void loop_handle_cmd(struct loop_
+ failed:
+ /* complete non-aio request */
+ if (!cmd->use_aio || ret) {
+- cmd->ret = ret ? -EIO : 0;
++ if (ret == -EOPNOTSUPP)
++ cmd->ret = ret;
++ else
++ cmd->ret = ret ? -EIO : 0;
+ blk_mq_complete_request(rq);
+ }
+ }
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