Re: [RFC PATCH v2 8/8] ext4: support dma-buf registered buffers for direct I/O

[sashiko-bot@kernel.org]

> From: Mengmeng Zhao <zhaomengmeng@kylinos.cn>
> 
> Advertise FMODE_CAN_DMABUF_IO for inodes that can support dma-buf I/O
> and implement ->init_dma_buf_io_ctx() by registering the buffer against
> the filesystem's block device.  The capability follows
> ext4_dio_alignment(), so an inode that can never do direct I/O -
> fs-verity, data=journal or inline data - is refused at open, and
> encrypted inodes are refused on the inode flag, which is set even
> without CONFIG_FS_ENCRYPTION.  The inode is rechecked at registration
> because DAX can be enabled after the file was opened.
> 
> A dma-buf iterator has no pages to copy from, so it must never reach the
> page cache.  ext4_buffered_read_iter() and ext4_buffered_write_iter() are
> the single sinks of the buffered fallbacks and refuse it there; a short
> direct I/O write still reports its progress, and the DAX write path
> refuses at its entry instead of after starting a journal handle.
> 
> Signed-off-by: Mengmeng Zhao <zhaomengmeng@kylinos.cn>
> Signed-off-by: Li Wang <liwang@kylinos.cn>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261113070621.273953-1-mengmeng.zhao@linux.dev?part=8