Commit b29dca44 authored Dec 02, 2020 by Qu Wenruo Committed by David Sterba Dec 09, 2020

btrfs: scrub: support subpage data scrub



Btrfs scrub is more flexible than buffered data write path, as we can
read an unaligned subpage data into page offset 0.

This ability makes subpage support much easier, we just need to check
each scrub_page::page_len and ensure we only calculate hash for [0,
page_len) of a page.

There is a small thing to notice: for subpage case, we still do sector
by sector scrub.  This means we will submit a read bio for each sector
to scrub, resulting in the same amount of read bios, just like on the 4K
page systems.

This behavior can be considered as a good thing, if we want everything
to be the same as 4K page systems.  But this also means, we're wasting
the possibility to submit larger bio using 64K page size.  This is
another problem to consider in the future.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

parent 53f3251d

fs/btrfs/scrub.c

+7 −3

Original line number	Diff line number	Diff line
		@@ -1795,11 +1795,15 @@ static int scrub_checksum_data(struct scrub_block *sblock)

		shash->tfm = fs_info->csum_shash;
		crypto_shash_init(shash);
		crypto_shash_digest(shash, kaddr, PAGE_SIZE, csum);

		if (memcmp(csum, spage->csum, sctx->fs_info->csum_size))
		sblock->checksum_error = 1;
		/*
		* In scrub_pages() and scrub_pages_for_parity() we ensure each spage
		* only contains one sector of data.
		*/
		crypto_shash_digest(shash, kaddr, fs_info->sectorsize, csum);

		if (memcmp(csum, spage->csum, fs_info->csum_size))
		sblock->checksum_error = 1;
		return sblock->checksum_error;
		}

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