Commit 4ced85f8 authored by Qu Wenruo's avatar Qu Wenruo Committed by David Sterba
Browse files

btrfs: reduce type width of btrfs_io_contexts 



That structure is our ultimate object for all __btrfs_map_block()
related functions.  We have some hard to understand members, like
tgtdev_map, but without any comments.

This patch will improve the situation:

- Add extra comments for num_stripes, mirror_num, num_tgtdevs and
  tgtdev_map[]
  Especially for the last two members, add a dedicated (thus very long)
  comments for them, with example to explain it.

- Shrink those int members to u16.
  In fact our on-disk format is only using u16 for num_stripes, thus
  no need to use int at all.

Signed-off-by: default avatarQu Wenruo <wqu@suse.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent be5c7edb

fs/btrfs/volumes.c

+9 −7
Original line number Diff line number Diff line
@@ -5914,16 +5914,18 @@ static void sort_parity_stripes(struct btrfs_io_context *bioc, int num_stripes) 
}



static struct btrfs_io_context *alloc_btrfs_io_context(struct btrfs_fs_info *fs_info,

						       int total_stripes,

						       int real_stripes)

						       u16 total_stripes,

						       u16 real_stripes)

{

	struct btrfs_io_context *bioc = kzalloc(

	struct btrfs_io_context *bioc;



	bioc = kzalloc(

		 /* The size of btrfs_io_context */

		sizeof(struct btrfs_io_context) +

		/* Plus the variable array for the stripes */

		sizeof(struct btrfs_io_stripe) * (total_stripes) +

		/* Plus the variable array for the tgt dev */

		sizeof(int) * (real_stripes) +

		sizeof(u16) * (real_stripes) +

		/*

		 * Plus the raid_map, which includes both the tgt dev

		 * and the stripes.
@@ -5937,7 +5939,7 @@ static struct btrfs_io_context *alloc_btrfs_io_context(struct btrfs_fs_info *fs_ 
	refcount_set(&bioc->refs, 1);



	bioc->fs_info = fs_info;

	bioc->tgtdev_map = (int *)(bioc->stripes + total_stripes);

	bioc->tgtdev_map = (u16 *)(bioc->stripes + total_stripes);

	bioc->raid_map = (u64 *)(bioc->tgtdev_map + real_stripes);



	return bioc;
@@ -6370,12 +6372,12 @@ int __btrfs_map_block(struct btrfs_fs_info *fs_info, enum btrfs_map_op op, 
	int mirror_num = (mirror_num_ret ? *mirror_num_ret : 0);

	int num_stripes;

	int max_errors = 0;

	int tgtdev_indexes = 0;

	struct btrfs_io_context *bioc = NULL;

	struct btrfs_dev_replace *dev_replace = &fs_info->dev_replace;

	int dev_replace_is_ongoing = 0;

	int num_alloc_stripes;

	int patch_the_first_stripe_for_dev_replace = 0;

	u16 num_alloc_stripes;

	u16 tgtdev_indexes = 0;

	u64 physical_to_patch_in_first_stripe = 0;

	u64 raid56_full_stripe_start = (u64)-1;

	u64 max_len;

fs/btrfs/volumes.h

+49 −5
Original line number Diff line number Diff line
@@ -408,11 +408,55 @@ struct btrfs_io_context { 
	u64 map_type; /* get from map_lookup->type */

	struct bio *orig_bio;

	atomic_t error;

	int max_errors;

	int num_stripes;

	int mirror_num;

	int num_tgtdevs;

	int *tgtdev_map;

	u16 max_errors;



	/*

	 * The total number of stripes, including the extra duplicated

	 * stripe for replace.

	 */

	u16 num_stripes;



	/*

	 * The mirror_num of this bioc.

	 *

	 * This is for reads which use 0 as mirror_num, thus we should return a

	 * valid mirror_num (>0) for the reader.

	 */

	u16 mirror_num;



	/*

	 * The following two members are for dev-replace case only.

	 *

	 * @num_tgtdevs:	Number of duplicated stripes which need to be

	 *			written to replace target.

	 *			Should be <= 2 (2 for DUP, otherwise <= 1).

	 * @tgtdev_map:		The array indicates where the duplicated stripes

	 *			are from. The size is the number of original

	 *			stripes (num_stripes - num_tgtdevs).

	 *

	 * The @tgtdev_map[] array is mostly for RAID56 cases.

	 * As non-RAID56 stripes share the same contents of the mapped range,

	 * thus no need to bother where the duplicated ones are from.

	 *

	 * But for RAID56 case, all stripes contain different contents, thus

	 * we need a way to know the mapping.

	 *

	 * There is an example for the two members, using a RAID5 write:

	 *

	 *   num_stripes:	4 (3 + 1 duplicated write)

	 *   stripes[0]:	dev = devid 1, physical = X

	 *   stripes[1]:	dev = devid 2, physical = Y

	 *   stripes[2]:	dev = devid 3, physical = Z

	 *   stripes[3]:	dev = devid 0, physical = Y

	 *

	 * num_tgtdevs = 1

	 * tgtdev_map[0] = 0	<- Means stripes[0] is not involved in replace.

	 * tgtdev_map[1] = 3	<- Means stripes[1] is involved in replace,

	 *			   and it's duplicated to stripes[3].

	 * tgtdev_map[2] = 0	<- Means stripes[2] is not involved in replace.

	 */

	u16 num_tgtdevs;

	u16 *tgtdev_map;

	/*

	 * logical block numbers for the start of each stripe

	 * The last one or two are p/q.  These are sorted,