Re: [PATCH 2/4 v2] btrfs-progs: mechanism to fetch fsinfo from btrfs-control

[Josef Bacik <jbacik@fusionio.com>]

On Mon, Nov 04, 2013 at 11:45:43AM +0800, Anand Jain wrote:
> need fsinfo from btrfs-control that is when mount path is
> not known.
> current method of going through each mount points isn't
> efficient, and multiple subvol of a fsid could be mounted
> means extra logic to handle that. Further this will help
> to revamp check_mounted() (planned)
> 
> check_mounted is heavily used in the btrfs-progs, it
> does full scan of all the disks in the system to confirm
> if a multi-disk btrfs is mounted it doesn't scalable well
> with few hundreds luns, check_mounted for sure needs a
> revamp. using this it can be done easily. which is planned.
> 
> v2: commit reword
> 
> Signed-off-by: Anand Jain <anand.jain@oracle.com>
> ---
>  ioctl.h |   19 +++++++++++++++
>  utils.c |   80 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  utils.h |    1 +
>  3 files changed, 100 insertions(+), 0 deletions(-)
> 
> diff --git a/ioctl.h b/ioctl.h
> index d21413f..29575d8 100644
> --- a/ioctl.h
> +++ b/ioctl.h
> @@ -506,6 +506,23 @@ static inline char *btrfs_err_str(enum btrfs_err_code err_code)
>  	}
>  }
>  
> +/* fs flags */
> +#define BTRFS_FS_MOUNTED	(1LLU << 0)
> +
> +struct btrfs_ioctl_fslist {
> +	__u64 self_sz;			/* in/out */
> +	__u8 fsid[BTRFS_FSID_SIZE];	/* out */
> +	__u64 num_devices;
> +	__u64 missing_devices;
> +	__u64 total_devices;
> +	__u64 flags;
> +};
> +
> +struct btrfs_ioctl_fslist_args {
> +	__u64 self_sz;		/* in/out */
> +	__u64 count;		/* out */
> +};
> +
>  #define BTRFS_IOC_SNAP_CREATE _IOW(BTRFS_IOCTL_MAGIC, 1, \
>  				   struct btrfs_ioctl_vol_args)
>  #define BTRFS_IOC_DEFRAG _IOW(BTRFS_IOCTL_MAGIC, 2, \
> @@ -604,6 +621,8 @@ struct btrfs_ioctl_clone_range_args {
>  				    struct btrfs_ioctl_dev_replace_args)
>  #define BTRFS_IOC_DEDUP_CTL _IOWR(BTRFS_IOCTL_MAGIC, 55, \
>  				  struct btrfs_ioctl_dedup_args)
> +#define BTRFS_IOC_GET_FSLIST _IOWR(BTRFS_IOCTL_MAGIC, 56, \
> +					struct btrfs_ioctl_fslist_args)
>  #ifdef __cplusplus
>  }
>  #endif
> diff --git a/utils.c b/utils.c
> index 5bedd97..1798a7c 100644
> --- a/utils.c
> +++ b/utils.c
> @@ -2087,3 +2087,83 @@ int lookup_ino_rootid(int fd, u64 *rootid)
>  
>  	return 0;
>  }
> +
> +/* scans for fsid(s) in the kernel using the btrfs-control
> + * interface.
> + */
> +int get_fslist(struct btrfs_ioctl_fslist **out_fslist, int *out_count)
> +{
> +	int ret, fd, e;
> +	struct btrfs_ioctl_fslist_args *fsargs;
> +	struct btrfs_ioctl_fslist *fslist;
> +	struct btrfs_ioctl_fslist *fslist_tmp;
> +	u64 sz;
> +	int count;
> +
> +	fd = open("/dev/btrfs-control", O_RDWR);
> +	e = errno;
> +	if (fd < 0) {
> +		perror("failed to open /dev/btrfs-control");
> +		return -e;
> +	}
> +
> +	/* space to hold 512 fsids, doesn't matter if small
> +	 * it would fail and return count so then we try again
> +	 */
> +	count = 512;
> +again:
> +	sz = sizeof(*fsargs) + sizeof(*fslist) * count;
> +
> +	fsargs = (struct btrfs_ioctl_fslist_args *) malloc(sz);

No need to cast the return value of malloc.

> +	memset(fsargs, 0, sz);
> +
> +	if (!fsargs) {
> +		close(fd);
> +		return -ENOMEM;
> +	}

Should check !fsargs before memsetting it.

> +	fsargs->count = count;
> +
> +	ret = ioctl(fd, BTRFS_IOC_GET_FSLIST, fsargs);
> +	e = errno;
> +	if (ret == 1) {
> +		/* out of size so reallocate */
> +		count = fsargs->count;
> +		free(fsargs);
> +		goto again;
> +	} else if (ret < 0) {
> +		printf("ERROR: scan_fsid ioctl failed - %s\n",
> +			strerror(e));
> +		ret = -e;
> +		goto out;
> +	}
> +
> +	/* ioctl returns fsid count in count parameter*/
> +
> +	*out_count = count = fsargs->count;
> +	if (count == 0) {
> +		*out_fslist = NULL;
> +		ret = 0;
> +		goto out;
> +	}
> +
> +	fslist = (struct btrfs_ioctl_fslist *) (fsargs +
> +						sizeof(*fsargs));
> +
> +	fslist_tmp = *out_fslist = (struct btrfs_ioctl_fslist *)
> +				malloc(sizeof(*fslist) * count);

No need to cast.  Thanks,

Josef