ACK/Cmnt: [SRU][Q][PATCH 1/1] UBUNTU: SAUCE: Revert "ext4: fail unaligned direct IO write with EINVAL"

[Stefan Bader]

On 08/01/2026 11:25, Edoardo Canepa wrote:
> BugLink: https://bugs.launchpad.net/bugs/2137698
> 
> This reverts commit 6c840c16c7cc0d3464ebf4a6d4c4f03763a45ff0.
> 
> This commit was pulled from stable upstream 6.17.4, however makes the
> ubuntu_blktrace_smoke_test fail as reported in the launchpad bug
> when performed by rust coreutils
> 
> Signed-off-by: Edoardo Canepa <edoardo.canepa at canonical.com>

Acked-by: Stefan Bader <stefan.bader at canonical.com>
> ---

Long-term we probably want to drop the revert but for now it makes sense 
to move back to previous behavior until we know why rust-coreutils fail 
with it.

>   fs/ext4/inode.c | 35 +++++++++++++++++++++++++++++++++++
>   1 file changed, 35 insertions(+)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index f9e4ac87211e..79422c6f664c 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3872,12 +3872,47 @@ static int ext4_iomap_overwrite_begin(struct inode *inode, loff_t offset,
>   	return ret;
>   }
>   
> +static inline bool ext4_want_directio_fallback(unsigned flags, ssize_t written)
> +{
> +	/* must be a directio to fall back to buffered */
> +	if ((flags & (IOMAP_WRITE | IOMAP_DIRECT)) !=
> +		    (IOMAP_WRITE | IOMAP_DIRECT))
> +		return false;
> +
> +	/* atomic writes are all-or-nothing */
> +	if (flags & IOMAP_ATOMIC)
> +		return false;
> +
> +	/* can only try again if we wrote nothing */
> +	return written == 0;
> +}
> +
> +static int ext4_iomap_end(struct inode *inode, loff_t offset, loff_t length,
> +			  ssize_t written, unsigned flags, struct iomap *iomap)
> +{
> +	/*
> +	 * Check to see whether an error occurred while writing out the data to
> +	 * the allocated blocks. If so, return the magic error code for
> +	 * non-atomic write so that we fallback to buffered I/O and attempt to
> +	 * complete the remainder of the I/O.
> +	 * For non-atomic writes, any blocks that may have been
> +	 * allocated in preparation for the direct I/O will be reused during
> +	 * buffered I/O. For atomic write, we never fallback to buffered-io.
> +	 */
> +	if (ext4_want_directio_fallback(flags, written))
> +		return -ENOTBLK;
> +
> +	return 0;
> +}
> +
>   const struct iomap_ops ext4_iomap_ops = {
>   	.iomap_begin		= ext4_iomap_begin,
> +	.iomap_end		= ext4_iomap_end,
>   };
>   
>   const struct iomap_ops ext4_iomap_overwrite_ops = {
>   	.iomap_begin		= ext4_iomap_overwrite_begin,
> +	.iomap_end		= ext4_iomap_end,
>   };
>   
>   static int ext4_iomap_begin_report(struct inode *inode, loff_t offset,

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