block: save user max_sectors limit

The user can set the max_sectors limit to any valid value via sysfs
/sys/block/<dev>/queue/max_sectors_kb attribute. If the device limits
are ever rescanned, though, the limit reverts back to the potentially
artificially low BLK_DEF_MAX_SECTORS value.

Preserve the user's setting as the max_sectors limit as long as it's
valid. The user can reset back to defaults by writing 0 to the sysfs
file.

Signed-off-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Link: https://lore.kernel.org/r/20230105205146.3610282-3-kbusch@meta.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/Documentation/ABI/stable/sysfs-block b/Documentation/ABI/stable/sysfs-block
index cd14ecb..ac1e519 100644 (file)
--- a/Documentation/ABI/stable/sysfs-block
+++ b/Documentation/ABI/stable/sysfs-block
@@ -432,7 +432,8 @@ Contact:    linux-block@vger.kernel.org
 Description:
                [RW] This is the maximum number of kilobytes that the block
                layer will allow for a filesystem request. Must be smaller than
-               or equal to the maximum size allowed by the hardware.
+               or equal to the maximum size allowed by the hardware. Write 0
+               to use default kernel settings.
 
 
 What:          /sys/block/<disk>/queue/max_segment_size

diff --git a/block/blk-settings.c b/block/blk-settings.c
index 9875ca1..9c9713c 100644 (file)
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -40,7 +40,7 @@ void blk_set_default_limits(struct queue_limits *lim)
        lim->virt_boundary_mask = 0;
        lim->max_segment_size = BLK_MAX_SEGMENT_SIZE;
        lim->max_sectors = lim->max_hw_sectors = BLK_SAFE_MAX_SECTORS;
-       lim->max_dev_sectors = 0;
+       lim->max_user_sectors = lim->max_dev_sectors = 0;
        lim->chunk_sectors = 0;
        lim->max_write_zeroes_sectors = 0;
        lim->max_zone_append_sectors = 0;
@@ -135,7 +135,12 @@ void blk_queue_max_hw_sectors(struct request_queue *q, unsigned int max_hw_secto
        limits->max_hw_sectors = max_hw_sectors;
 
        max_sectors = min_not_zero(max_hw_sectors, limits->max_dev_sectors);
-       max_sectors = min(max_sectors, BLK_DEF_MAX_SECTORS);
+
+       if (limits->max_user_sectors)
+               max_sectors = min(max_sectors, limits->max_user_sectors);
+       else
+               max_sectors = min(max_sectors, BLK_DEF_MAX_SECTORS);
+
        max_sectors = round_down(max_sectors,
                                 limits->logical_block_size >> SECTOR_SHIFT);
        limits->max_sectors = max_sectors;

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 93d9e9c..5486b6c 100644 (file)
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -239,19 +239,28 @@ static ssize_t queue_zone_append_max_show(struct request_queue *q, char *page)
 static ssize_t
 queue_max_sectors_store(struct request_queue *q, const char *page, size_t count)
 {
-       unsigned long max_sectors_kb,
+       unsigned long var;
+       unsigned int 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 = queue_var_store(&var, page, count);
 
        if (ret < 0)
                return ret;
 
-       max_hw_sectors_kb = min_not_zero(max_hw_sectors_kb, (unsigned long)
+       max_sectors_kb = (unsigned int)var;
+       max_hw_sectors_kb = min_not_zero(max_hw_sectors_kb,
                                         q->limits.max_dev_sectors >> 1);
-
-       if (max_sectors_kb > max_hw_sectors_kb || max_sectors_kb < page_kb)
-               return -EINVAL;
+       if (max_sectors_kb == 0) {
+               q->limits.max_user_sectors = 0;
+               max_sectors_kb = min(max_hw_sectors_kb,
+                                    BLK_DEF_MAX_SECTORS >> 1);
+       } else {
+               if (max_sectors_kb > max_hw_sectors_kb ||
+                   max_sectors_kb < page_kb)
+                       return -EINVAL;
+               q->limits.max_user_sectors = max_sectors_kb << 1;
+       }
 
        spin_lock_irq(&q->queue_lock);
        q->limits.max_sectors = max_sectors_kb << 1;

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 2b85161..b87ed82 100644 (file)
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -288,6 +288,7 @@ struct queue_limits {
        unsigned int            max_dev_sectors;
        unsigned int            chunk_sectors;
        unsigned int            max_sectors;
+       unsigned int            max_user_sectors;
        unsigned int            max_segment_size;
        unsigned int            physical_block_size;
        unsigned int            logical_block_size;