On Mon, Dec 27, 2021 at 08:54:28PM +0800, Jeffle Xu wrote:
> Until then erofs is exactly blockdev based filesystem. In other using
> scenarios (e.g. container image), erofs needs to run upon files.
>
> This patch introduces a new nodev mode, in which erofs could be mounted
> from a bootstrap blob file containing the complete erofs image.
>
> The following patch will introduce a new mount option "uuid", by which
> users could specify the bootstrap blob file.
>
> Signed-off-by: Jeffle Xu <jefflexu@xxxxxxxxxxxxxxxxx>
I think the order of some patches in this patchset can be improved.
Take this patch as an example. This patch introduces a new mount
option called "uuid", so the kernel will just accept it (which
generates a user-visible impact) after this patch but it doesn't
actually work.
Therefore, we actually have three different behaviors here:
- kernel doesn't support "uuid" mount option completely;
- kernel support "uuid" but it doesn't work;
- kernel support "uuid" correctly (maybe after some random patch);
Actually that is bad for bisecting since there are some commits
having temporary behaviors. And we don't know which commit
actually fully implements this "uuid" mount option.
So personally I think the proper order is just like the bottom-up
approach, and make sure each patch can be tested / bisected
independently.
> ---
> fs/erofs/data.c | 13 ++++++++---
> fs/erofs/internal.h | 1 +
> fs/erofs/super.c | 56 +++++++++++++++++++++++++++++++++------------
> 3 files changed, 53 insertions(+), 17 deletions(-)
>
> diff --git a/fs/erofs/data.c b/fs/erofs/data.c
> index 477aaff0c832..61fa431d0713 100644
> --- a/fs/erofs/data.c
> +++ b/fs/erofs/data.c
> @@ -11,11 +11,18 @@
>
> struct page *erofs_get_meta_page(struct super_block *sb, erofs_blk_t blkaddr)
> {
> - struct address_space *const mapping = sb->s_bdev->bd_inode->i_mapping;
> + struct address_space *mapping;
> struct page *page;
>
> - page = read_cache_page_gfp(mapping, blkaddr,
> - mapping_gfp_constraint(mapping, ~__GFP_FS));
Apart from the recommendation above, if my understanding is
correct, I think after we implement fscache_aops,
read_cache_page_gfp() can work with proper fscache mapping.
So no need to implement something like erofs_readpage_from_fscache()
later (at least for the case here.)
Thanks,
Gao Xiang
> + if (sb->s_bdev) {
> + mapping = sb->s_bdev->bd_inode->i_mapping;
> + page = read_cache_page_gfp(mapping, blkaddr,
> + mapping_gfp_constraint(mapping, ~__GFP_FS));
> + } else {
> + /* TODO: data path in nodev mode */
> + page = ERR_PTR(-EINVAL);
> + }
> +
--
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