Messages in this thread | | | From | Daeho Jeong <> | Date | Wed, 21 Jul 2021 15:30:46 -0700 | Subject | Re: [f2fs-dev] [PATCH] f2fs: change fiemap way in printing compression chunk |
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Hi Eric,
On Wed, Jul 21, 2021 at 2:35 PM Eric Biggers <ebiggers@kernel.org> wrote: > > On Wed, Jul 21, 2021 at 12:20:48AM -0700, Daeho Jeong wrote: > > From: Daeho Jeong <daehojeong@google.com> > > > > When we print out a discontinuous compression chunk, it shows like a > > continuous chunk now. To show it more correctly, I've changed the way of > > printing fiemap info like below. Plus, eliminated NEW_ADDR(-1) in fiemap > > info, since it is not in fiemap user api manual. > > > > 0: 0000000000000000 0000000000000000 0000000000001000 1008 (M/E) > > 1: 0000000000001000 0000000f15c0f000 0000000000001000 1008 (M/E) > > 2: 0000000000002000 0000000000000000 0000000000002000 1808 (M/U/E) > > 3: 0000000000004000 0000000000000000 0000000000001000 1008 (M/E) > > 4: 0000000000005000 0000000f15c10000 0000000000001000 1008 (M/E) > > 5: 0000000000006000 0000000000000000 0000000000002000 1808 (M/U/E) > > 6: 0000000000008000 0000000000000000 0000000000001000 1008 (M/E) > > Please label these columns. > > Anyway, this doesn't appear to work quite in the way I had in mind. With this > patch, what I'm seeing is: > > $ head -c 16384 /dev/zero > file; xfs_io -c "fiemap -v" file > file: > EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS > 0: [0..7]: 0..7 8 0x1008 > 1: [8..15]: 2683128..2683135 8 0x1008 > 2: [16..31]: 0..15 16 0x1809 > > So, working in 512-byte sectors, the logical sectors 0-31 are stored as one > compressed cluster in the 8 physical sectors 2683128-2683135. > > The problem is, with this patch these physical sectors are reported at logical > sectors 8-15 instead of 0-7. Obviously, this isn't particularly well-defined, > but I thought it was logical for the physical blocks to be associated with the > first logical blocks. That is what the tests I've written (xfstest f2fs/002, > and the Android vts_kernel_encryption_test) assume. > > Is there any particular reason why you wouldn't report instead: > > 0: [0..7]: 2683128..2683135 8 0x1008 > 1: [8..31]: 0..23 8 0x1809 > > - Eric
The reason is related to how F2FS stores the mapping information in the mapping table. Actually, the mapping inside of the table is like this. [0..7]: COMPR_ADDR flag(0x1008) -> merged, encoded [8..15]: 2683128..2683135 flag(0x1008) -> merged, encoded [16..31]: NEW_ADDR flag(0x1809) -> merged, unwritten(!), last_extent
I understand what you mean. But, if we adapt to your way, how do you think we can print out when we ask for f2fs to print out only the [8..15] area? Zero address? How about flags? I think the current way explains the layout of the f2fs metadata more exactly.
Thank you,
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