dm-verity: make dm_verity_fec_io::bufs variable-length

Browse source

When correcting a data block, the FEC code performs optimally when it
has enough buffers to hold all the needed RS blocks.  That number of
buffers is '1 << (v->data_dev_block_bits - DM_VERITY_FEC_BUF_RS_BITS)'.

However, since v->data_dev_block_bits isn't a compile-time constant, the
code actually used PAGE_SHIFT instead.

With the traditional PAGE_SIZE == data_block_size == 4096, this was
fine.  However, when PAGE_SIZE > data_block_size, this wastes space.
E.g., with data_block_size == 4096 && PAGE_SIZE == 16384, struct
dm_verity_fec_io is 9240 bytes, when in fact only 3096 bytes are needed.

Fix this by making dm_verity_fec_io::bufs a variable-length array.

This makes the macros DM_VERITY_FEC_BUF_MAX and
fec_for_each_extra_buffer() no longer apply, so remove them.  For
consistency, and because DM_VERITY_FEC_BUF_PREALLOC is fixed at 1 and
was already assumed to be 1 (considering that mempool_alloc() shouldn't
be called in a loop), also remove the related macros
DM_VERITY_FEC_BUF_PREALLOC and fec_for_each_prealloc_buffer().

Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

...

This commit is contained in:

Eric Biggers 2025-12-19 11:29:04 -08:00 • committed by Mikulas Patocka

parent b140a921ea

commit 533e641b45

2 changed files with 31 additions and 28 deletions

Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL

Download patch file Download diff file Expand all files Collapse all files

44

drivers/md/dm-verity-fec.c

View file

15

drivers/md/dm-verity-fec.h

View file