Motivation: When fs data/metadata checksum mismatch, lower block devices may have other correct copies. e.g. If XFS successfully reads a metadata buffer off a raid1 but decides that the metadata is garbage, today it will shut down the entire filesystem without trying any of the other mirrors. This is a severe loss of service, and we propose these patches to have XFS try harder to avoid failure. This patch prototype this mirror retry idea by: * Adding @nr_mirrors to struct request_queue which is similar as blk_queue_nonrot(), filesystem can grab device request queue and check max mirrors this block device has. Helper functions were also added to get/set the nr_mirrors. * Introducing bi_rd_hint just like bi_write_hint, but bi_rd_hint is a long bitmap in order to support stacked layer case. * Modify md/raid1 to support this retry feature. * Adapter xfs to use this feature. If the read verify fails, we loop over the available mirrors and retry the read. * Rewrite retried read When the read verification fails, but the retry succeedes write the buffer back to correct the bad mirror * Add tracepoints and logging to alternate device retry. This patch adds new log entries and trace points to the alternate device retry error path. Changes v2: - No more reuse bi_write_hint - Stacked layer support(see patch 4/9) - Other feedback fix Allison Henderson (5): Add b_alt_retry to xfs_buf xfs: Add b_rd_hint to xfs_buf xfs: Add device retry xfs: Rewrite retried read xfs: Add tracepoints and logging to alternate device retry Bob Liu (4): block: add nr_mirrors to request_queue block: add rd_hint to bio and request md:raid1: set mirrors correctly md:raid1: rd_hint support and consider stacked layer case Documentation/block/biodoc.txt | 3 + block/bio.c | 1 + block/blk-core.c | 4 ++ block/blk-merge.c | 6 ++ block/blk-settings.c | 24 +++++++ block/bounce.c | 1 + drivers/md/raid1.c | 123 ++++++++++++++++++++++++++++++++- fs/xfs/xfs_buf.c | 58 +++++++++++++++- fs/xfs/xfs_buf.h | 14 ++++ fs/xfs/xfs_trace.h | 6 +- include/linux/blk_types.h | 1 + include/linux/blkdev.h | 4 ++ include/linux/types.h | 3 + 13 files changed, 244 insertions(+), 4 deletions(-) -- 2.17.1
