Otherwise users can easily shoot themselves in the foot by creating the situation where the top-level stacked device (e.g. DM multipath) has a larger max_sectors_kb than the underlying device(s). Which will certainly lead to IO errors due to the "over max size limit" check in blk_cloned_rq_check_limits(). Use of WARN_ON_ONCE() gives users visibility into which application attempted to perform this unsupported max_sectors_kb change. This is a crude, yet effective, solution that forces the use of system software (e.g. udev rules or multipathd) to tweak max_sectors_kb of the underlying devices _before_ a layer like DM multipath is layered ontop. Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx> --- block/blk-sysfs.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index 9cc8d7c..cce43d7 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -199,8 +199,12 @@ queue_max_sectors_store(struct request_queue *q, const char *page, size_t count) unsigned long max_sectors_kb, max_hw_sectors_kb = queue_max_hw_sectors(q) >> 1, page_kb = 1 << (PAGE_SHIFT - 10); - ssize_t ret = queue_var_store(&max_sectors_kb, page, count); + ssize_t ret; + + if (WARN_ON_ONCE(blk_queue_stackable(q))) + return -EINVAL; + ret = queue_var_store(&max_sectors_kb, page, count); if (ret < 0) return ret; -- 2.8.4 (Apple Git-73) -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
