From 72e4996a54fe54b93bf1e667a5e60099375fe08f Mon Sep 17 00:00:00 2001 From: Rob N Date: Sat, 13 Apr 2024 02:00:20 +1000 Subject: [PATCH] bdev_discard_supported: understand discard_granularity=0 Kernel documentation for the discard_granularity property says: A discard_granularity of 0 means that the device does not support discard functionality. Some older kernels had drivers (notably loop, but also some USB-SATA adapters) that would set the QUEUE_FLAG_DISCARD capability flag, but have discard_granularity=0. Since 5.10 (torvalds/linux@b35fd7422c2f) the discard entry point blkdev_issue_discard() has had a check for this, which would immediately reject the call with EOPNOTSUPP, and throw a scary diagnostic message into the log. See #16068. Since 6.8, the block layer sets a non-zero default for discard_granularity (torvalds/linux@3c407dc723bb), and a future kernel will remove the check entirely[1]. As such, there's no good reason for us to enable discard when discard_granularity=0. The kernel will never let the request go in anyway; better that we just disable it so we can report it properly to the user. 1. https://patchwork.kernel.org/project/linux-block/patch/20240312144826.1045212-2-hch@lst.de/ Sponsored-by: Klara, Inc. Sponsored-by: Wasabi Technology, Inc. Signed-off-by: Rob Norris (cherry picked from commit b181b2e604de3f36feab1092c702cdec5e78c693) --- include/os/linux/kernel/linux/blkdev_compat.h | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/include/os/linux/kernel/linux/blkdev_compat.h b/include/os/linux/kernel/linux/blkdev_compat.h index f111e648c..b0f398354 100644 --- a/include/os/linux/kernel/linux/blkdev_compat.h +++ b/include/os/linux/kernel/linux/blkdev_compat.h @@ -563,9 +563,11 @@ static inline boolean_t bdev_discard_supported(struct block_device *bdev) { #if defined(HAVE_BDEV_MAX_DISCARD_SECTORS) - return (!!bdev_max_discard_sectors(bdev)); + return (bdev_max_discard_sectors(bdev) > 0 && + bdev_discard_granularity(bdev) > 0); #elif defined(HAVE_BLK_QUEUE_DISCARD) - return (!!blk_queue_discard(bdev_get_queue(bdev))); + return (blk_queue_discard(bdev_get_queue(bdev)) > 0 && + bdev_get_queue(bdev)->limits.discard_granularity > 0); #else #error "Unsupported kernel" #endif