Re: [PATCH] dm-cache: Add handle to contlr if cache_create failed.

[Alasdair G Kergon <agk@redhat.com>]

Current pahole output (offsets/size on right):

struct cache_disk_superblock {
	__le32                     csum;                 /*     0     4 */
	__le32                     flags;                /*     4     4 */
	__le64                     blocknr;              /*     8     8 */
	__u8                       uuid[16];             /*    16    16 */
	__le64                     magic;                /*    32     8 */
	__le32                     version;              /*    40     4 */
	__u8                       policy_name[16];      /*    44    16 */
	__le32                     policy_hint_size;     /*    60     4 */
	/* --- cacheline 1 boundary (64 bytes) --- */
	__u8                       metadata_space_map_root[128]; /*    64   128 */
	/* --- cacheline 3 boundary (192 bytes) --- */
	__le64                     mapping_root;         /*   192     8 */
	__le64                     hint_root;            /*   200     8 */
	__le64                     discard_root;         /*   208     8 */
	__le64                     discard_block_size;   /*   216     8 */
	__le64                     discard_nr_blocks;    /*   224     8 */
	__le32                     data_block_size;      /*   232     4 */
	__le32                     metadata_block_size;  /*   236     4 */
	__le32                     cache_blocks;         /*   240     4 */
	__le32                     compat_flags;         /*   244     4 */
	__le32                     compat_ro_flags;      /*   248     4 */
	__le32                     incompat_flags;       /*   252     4 */
	/* --- cacheline 4 boundary (256 bytes) --- */
	__le32                     read_hits;            /*   256     4 */
	__le32                     read_misses;          /*   260     4 */
	__le32                     write_hits;           /*   264     4 */
	__le32                     write_misses;         /*   268     4 */
	__le32                     policy_version[3];    /*   272    12 */

	/* size: 288, cachelines: 5, members: 25 */
	/* padding: 4 */
	/* last cacheline: 32 bytes */
};

Alasdair