[lxc-devel] [PATCH] Fix btrfs bus error on sparc on snapshot delete

[Serge Hallyn]

Quoting Thomas Tanaka (thomas.tanaka at oracle.com):
> The following patch fixes memory alignment and endianness
> issue while doing a snapshot deletion with btrfs as a
> backing store on platform such as sparc.
> 
> The implementation is taken from btrfs-progs.

Hi,

thanks, this looks nice.  I'm worried though that the #defines hide some of the
function definitions.  Can you add a brief comment listing the defined fns
names above their definitions in the .h file?

Where is bswap_64 defined?

> Signed-off-by: Thomas Tanaka <thomas.tanaka at oracle.com>
> ---
>  src/lxc/bdev/lxcbtrfs.c |   28 +++++++++++++++-------------
>  src/lxc/bdev/lxcbtrfs.h |   39 +++++++++++++++++++++++++++++++++++++++
>  2 files changed, 54 insertions(+), 13 deletions(-)
> 
> diff --git a/src/lxc/bdev/lxcbtrfs.c b/src/lxc/bdev/lxcbtrfs.c
> index 2db7c87..0f8c1fc 100644
> --- a/src/lxc/bdev/lxcbtrfs.c
> +++ b/src/lxc/bdev/lxcbtrfs.c
> @@ -565,7 +565,7 @@ static int btrfs_recursive_destroy(const char *path)
>  	int fd;
>  	struct btrfs_ioctl_search_args args;
>  	struct btrfs_ioctl_search_key *sk = &args.key;
> -	struct btrfs_ioctl_search_header *sh;
> +	struct btrfs_ioctl_search_header sh;
>  	struct btrfs_root_ref *ref;
>  	struct my_btrfs_tree *tree;
>  	int ret, i;
> @@ -573,6 +573,7 @@ static int btrfs_recursive_destroy(const char *path)
>  	int name_len;
>  	char *name;
>  	char *tmppath;
> +	u64 dir_id;
>  
>  	fd = open(path, O_RDONLY);
>  	if (fd < 0) {
> @@ -624,21 +625,22 @@ static int btrfs_recursive_destroy(const char *path)
>  
>  		off = 0;
>  		for (i = 0; i < sk->nr_items; i++) {
> -			sh = (struct btrfs_ioctl_search_header *)(args.buf + off);
> -			off += sizeof(*sh);
> +			memcpy(&sh, args.buf + off, sizeof(sh));
> +			off += sizeof(sh);
>  			/*
>  			 * A backref key with the name and dirid of the parent
>  			 * comes followed by the reoot ref key which has the
>  			 * name of the child subvol in question.
>  			 */
> -			if (sh->objectid != root_id && sh->type == BTRFS_ROOT_BACKREF_KEY) {
> +			if (sh.objectid != root_id && sh.type == BTRFS_ROOT_BACKREF_KEY) {
>  				ref = (struct btrfs_root_ref *)(args.buf + off);
> -				name_len = ref->name_len;
> +				name_len = btrfs_stack_root_ref_name_len(ref);
>  				name = (char *)(ref + 1);
> -				tmppath = get_btrfs_subvol_path(fd, sh->offset,
> -						ref->dirid, name, name_len);
> -				if (!add_btrfs_tree_node(tree, sh->objectid,
> -							sh->offset, name,
> +				dir_id = btrfs_stack_root_ref_dirid(ref);
> +				tmppath = get_btrfs_subvol_path(fd, sh.offset,
> +						dir_id, name, name_len);
> +				if (!add_btrfs_tree_node(tree, sh.objectid,
> +							sh.offset, name,
>  							name_len, tmppath)) {
>  					ERROR("Out of memory");
>  					free_btrfs_tree(tree);
> @@ -648,15 +650,15 @@ static int btrfs_recursive_destroy(const char *path)
>  				}
>  				free(tmppath);
>  			}
> -			off += sh->len;
> +			off += sh.len;
>  
>  			/*
>  			 * record the mins in sk so we can make sure the
>  			 * next search doesn't repeat this root
>  			 */
> -			sk->min_objectid = sh->objectid;
> -			sk->min_type = sh->type;
> -			sk->min_offset = sh->offset;
> +			sk->min_objectid = sh.objectid;
> +			sk->min_type = sh.type;
> +			sk->min_offset = sh.offset;
>  		}
>  		sk->nr_items = 4096;
>  		sk->min_offset++;
> diff --git a/src/lxc/bdev/lxcbtrfs.h b/src/lxc/bdev/lxcbtrfs.h
> index e0adb7a..4ea2b4a 100644
> --- a/src/lxc/bdev/lxcbtrfs.h
> +++ b/src/lxc/bdev/lxcbtrfs.h
> @@ -317,6 +317,45 @@ struct btrfs_ioctl_ino_lookup_args {
>  #define BTRFS_LAST_FREE_OBJECTID -256ULL
>  #define BTRFS_FIRST_CHUNK_TREE_OBJECTID 256ULL
>  
> +/* The followings are macro for correctly getting member of structures
> + * in both low and big endian platforms as per btrfs-progs 
> + */
> +#ifdef __CHECKER__
> +#define __force    __attribute__((force))
> +#else
> +#define __force
> +#endif
> +
> +#if __BYTE_ORDER == __BIG_ENDIAN
> +#define cpu_to_le64(x) ((__force __le64)(u64)(bswap_64(x)))
> +#define le64_to_cpu(x) ((__force u64)(__le64)(bswap_64(x)))
> +#define cpu_to_le32(x) ((__force __le32)(u32)(bswap_32(x)))
> +#define le32_to_cpu(x) ((__force u32)(__le32)(bswap_32(x)))
> +#define cpu_to_le16(x) ((__force __le16)(u16)(bswap_16(x)))
> +#define le16_to_cpu(x) ((__force u16)(__le16)(bswap_16(x)))
> +#else
> +#define cpu_to_le64(x) ((__force __le64)(u64)(x))
> +#define le64_to_cpu(x) ((__force u64)(__le64)(x))
> +#define cpu_to_le32(x) ((__force __le32)(u32)(x))
> +#define le32_to_cpu(x) ((__force u32)(__le32)(x))
> +#define cpu_to_le16(x) ((__force __le16)(u16)(x))
> +#define le16_to_cpu(x) ((__force u16)(__le16)(x))
> +#endif
> + 
> +#define BTRFS_SETGET_STACK_FUNCS(name, type, member, bits)              \
> +static inline u##bits btrfs_##name(type *s)                             \
> +{                                                                       \
> +        return le##bits##_to_cpu(s->member);                            \
> +}                                                                       \
> +static inline void btrfs_set_##name(type *s, u##bits val)               \
> +{                                                                       \
> +        s->member = cpu_to_le##bits(val);                               \
> +}
> +
> +BTRFS_SETGET_STACK_FUNCS(stack_root_ref_dirid, struct btrfs_root_ref, dirid, 64);
> +BTRFS_SETGET_STACK_FUNCS(stack_root_ref_sequence, struct btrfs_root_ref, sequence, 64);
> +BTRFS_SETGET_STACK_FUNCS(stack_root_ref_name_len, struct btrfs_root_ref, name_len, 16);
> +
>  /* defined in bdev.h */
>  struct bdev;
>  
> -- 
> 1.7.1
> 
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