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

[Anand Jain <Anand.Jain@oracle.com>]

Thanks sent out v3.

On 11/07/13 04:13 AM, Josef Bacik wrote:
> 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
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