> On Jun 14, 2023, at 11:48 PM, Christoph Hellwig <hch@xxxxxx> wrote:
>
> The support for write intent bitmaps in files on an external files in md
> is a hot mess that abuses ->bmap to map file offsets into physical device
> objects, and also abuses buffer_heads in a creative way.
>
> Make this code optional so that MD can be built into future kernels
> without buffer_head support, and so that we can eventually deprecate it.
>
> Note this does not affect the internal bitmap support, which has none of
> the problems.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
> drivers/md/Kconfig | 10 ++++++++++
> drivers/md/md-bitmap.c | 15 +++++++++++++++
> drivers/md/md.c | 7 +++++++
> 3 files changed, 32 insertions(+)
>
> diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
> index b0a22e99bade37..9712ab9bcba52e 100644
> --- a/drivers/md/Kconfig
> +++ b/drivers/md/Kconfig
> @@ -50,6 +50,16 @@ config MD_AUTODETECT
>
> If unsure, say Y.
>
> +config MD_BITMAP_FILE
> + bool "MD bitmap file support"
> + default y
> + help
> + If you say Y here, support for write intent bitmaps in files on an
> + external file system is enabled. This is an alternative to the internal
> + bitmaps near the MD superblock, and very problematic code that abuses
> + various kernel APIs and can only work with files on a file system not
> + actually sitting on the MD device.
> +
> config MD_LINEAR
> tristate "Linear (append) mode (deprecated)"
> depends on BLK_DEV_MD
> diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c
> index ed402f4dad182d..1e29088b1f081a 100644
> --- a/drivers/md/md-bitmap.c
> +++ b/drivers/md/md-bitmap.c
> @@ -295,6 +295,7 @@ static void write_sb_page(struct bitmap *bitmap, unsigned long pg_index,
>
> static void md_bitmap_file_kick(struct bitmap *bitmap);
>
> +#ifdef CONFIG_MD_BITMAP_FILE
> static void write_file_page(struct bitmap *bitmap, struct page *page, int wait)
> {
> struct buffer_head *bh = page_buffers(page);
> @@ -408,6 +409,20 @@ static int read_file_page(struct file *file, unsigned long index,
> ret);
> return ret;
> }
> +#else /* CONFIG_MD_BITMAP_FILE */
> +static void write_file_page(struct bitmap *bitmap, struct page *page, int wait)
> +{
> +}
> +static int read_file_page(struct file *file, unsigned long index,
> + struct bitmap *bitmap, unsigned long count, struct page *page)
> +{
> + return -EIO;
> +}
> +static void free_buffers(struct page *page)
> +{
> + put_page(page);
> +}
> +#endif /* CONFIG_MD_BITMAP_FILE */
>
> /*
> * bitmap file superblock operations
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index cf3733c90c47ed..c9fcefaf9c073b 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -7020,6 +7020,13 @@ static int set_bitmap_file(struct mddev *mddev, int fd)
>
> if (mddev->bitmap || mddev->bitmap_info.file)
> return -EEXIST; /* cannot add when bitmap is present */
> +
> + if (!IS_ENABLED(CONFIG_MD_BITMAP_FILE)) {
> + pr_warn("%s: bitmap files not supported by this kernel\n",
> + mdname(mddev));
> + return -EINVAL;
> + }
> +
> f = fget(fd);
>
> if (f == NULL) {
> --
> 2.39.2
>
Reviewed-by: Himanshu Madhani <himanshu.madhani@xxxxxxxxxx>
--
Himanshu Madhani Oracle Linux Engineering
