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

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Mon, Sep 21, 2026 at 04:28:14PM +0200, Niklas Cassel wrote:
> 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(-)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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