[PATCH v6 12/15] block: remove BlockLimits.max_append_sectors

[Niklas Cassel <cassel@kernel.org>]

The field described the largest zone append that a backend accepts. It
had one writer and one reader, and neither is left.

file-posix filled it from the zone_append_max_bytes queue attribute,
which bounds REQ_OP_ZONE_APPEND, an operation it never issues: Linux has
no userspace interface for one, so raw_co_zone_append() substitutes the
write pointer of the zone for the offset and the request reaches the
host as a plain pwritev().

The transfer limit does not apply either, no more than it does to an
ordinary write. This driver reports max_hw_transfer but never sets
BlockLimits.max_transfer, which is what bdrv_aligned_pwritev() splits
by, so a request of any size goes to the host kernel whole and is split
there: on a null_blk device whose zone_append_max_bytes is 130560, a
16 MiB append completes and advances the write pointer by 16 MiB. That
is safe for a sequential zone, as Linux issues the fragments of a split
write in order, with zone write plugging since 6.10 and zone write
locking before that.

virtio-blk was the reader, and now takes what it reports to a guest from
a property instead.

Remove the field and the assignment that filled it. Keeping it would be
worse than not having it: a driver that set it, believing something
enforced it, would be silently ignored.

Signed-off-by: Niklas Cassel <cassel@kernel.org>
---
 block/file-posix.c               | 5 -----
 include/block/block_int-common.h | 3 ---
 2 files changed, 8 deletions(-)

diff --git a/block/file-posix.c b/block/file-posix.c
index c1ac49d23d..1a4ca9d942 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -1488,11 +1488,6 @@ static void raw_refresh_zoned_limits(BlockDriverState *bs, struct stat *st,
     }
     bs->bl.nr_zones = ret;
 
-    ret = get_sysfs_long_val(st, "zone_append_max_bytes");
-    if (ret > 0) {
-        bs->bl.max_append_sectors = ret >> BDRV_SECTOR_BITS;
-    }
-
     ret = get_sysfs_long_val(st, "zone_write_granularity");
     if (ret >= 0) {
         bs->bl.write_granularity = ret;
diff --git a/include/block/block_int-common.h b/include/block/block_int-common.h
index 7abd2b12bb..cfc7b0f427 100644
--- a/include/block/block_int-common.h
+++ b/include/block/block_int-common.h
@@ -913,9 +913,6 @@ typedef struct BlockLimits {
     /* total number of zones */
     uint32_t nr_zones;
 
-    /* maximum sectors of a zone append write operation */
-    uint32_t max_append_sectors;
-
     /* maximum number of open zones */
     uint32_t max_open_zones;
 
-- 
2.55.0