Re: Bug in mkfs.btrfs?!

[Goffredo Baroncelli <kreijack@libero.it>]

On 01/23/2011 07:18 PM, Hugo Mills wrote:
>    Hi, Felix,
> 
> On Sat, Jan 22, 2011 at 04:56:12PM +0100, Felix Blanke wrote:
>> It was a simple:
>>
>> mkfs.btrfs -L backup -d single /dev/loop2
>>
>> But it also happens without the options, like:
>>
>> mkfs.btrfs /dev/loop2
>>
>>
>> /dev/loop2 is a loop device, which is aes encrypted. The output of "losetup /dev/loop2":
>>
>> /dev/loop2: [0010]:5324 
>> (/dev/disk/by-id/ata-WDC_WD6400AAKS-22A7B2_WD-WCASY7780706-part3) encryption=AES128
>>
>>
>> Thanks you for looking into this!
>> While writing this I read your second mail. The strace output is attached.
> 
>    OK, I've traced through the functions being called, and I really
> can't see where it could be truncating the name, unless your system
> has a stupidly small value of PATH_MAX.

It seems that when mkfs.btrfs checks if the passed block device is
already mounted, uses the ioctl LOOP_GET_STATUS [1]. This ioctl has as
argument the struct loop_info.

This ioctl, should return the info about the back-end of the loop
device. The file name is returned via the "lo_name" field, which is an
array of 64 char...[2]

Felix, what is the output of the following command ?

	/sbin/losetup -a

If my analysis is correct, this command should return the filename
trunked at the 64th character too.

Goffredo

[1] file util.c, function resolve_loop_device
[2]
http://lxr.e2g.org/source/bionic/libc/kernel/common/linux/loop.h?a=ppc#L26
  and
http://lxr.e2g.org/source/bionic/libc/kernel/common/linux/loop.h?a=ppc#L15





> 
>    Can you apply the following patch (to the "next" branch of the
> btrfs-progs git repo), rebuild, and try again? It's just adding some
> debugging output to track what it's looking at.
> 
>    Hugo.
> 
> 
> diff --git a/mkfs.c b/mkfs.c
> index 2e99b95..51a5096 100644
> --- a/mkfs.c
> +++ b/mkfs.c
> @@ -422,6 +422,7 @@ int main(int ac, char **av)
>  	printf("WARNING! - see http://btrfs.wiki.kernel.org before using\n\n");
>  
>  	file = av[optind++];
> +	printf("Checking whether %s is part of a mounted filesystem\n", file);
>  	ret = check_mounted(file);
>  	if (ret < 0) {
>  		fprintf(stderr, "error checking %s mount status\n", file);
> diff --git a/utils.c b/utils.c
> index fd894f3..7fa3149 100644
> --- a/utils.c
> +++ b/utils.c
> @@ -610,12 +610,16 @@ int resolve_loop_device(const char* loop_dev, char* loop_file, int max_len)
>  	int ret_ioctl;
>  	struct loop_info loopinfo;
>  
> +	printf("Resolving loop device %s (length %d)\n", loop_dev, max_len);
> +
>  	if ((loop_fd = open(loop_dev, O_RDONLY)) < 0)
>  		return -errno;
>  
>  	ret_ioctl = ioctl(loop_fd, LOOP_GET_STATUS, &loopinfo);
>  	close(loop_fd);
>  
> +	printf("Loop name = %s\n", loopinfo.lo_name);
> +
>  	if (ret_ioctl == 0)
>  		strncpy(loop_file, loopinfo.lo_name, max_len);
>  	else
> @@ -639,6 +643,9 @@ int is_same_blk_file(const char* a, const char* b)
>  		return -errno;
>  	}
>  
> +	printf("Realpath of %s was %s\n", a, real_a);
> +	printf("Realpath of %s was %s\n", b, real_b);
> +
>  	/* Identical path? */
>  	if(strcmp(real_a, real_b) == 0)
>  		return 1;
> @@ -680,6 +687,9 @@ int is_same_loop_file(const char* a, const char* b)
>  	const char* final_b;
>  	int ret;
>  
> +	printf("is_same_loop_file: %s and %s\n", a, b);
> +	printf("PATH_MAX = %d\n", PATH_MAX);
> +
>  	/* Resolve a if it is a loop device */
>  	if((ret = is_loop_device(a)) < 0) {
>  	   return ret;
> @@ -784,8 +794,10 @@ int check_mounted(const char* file)
>  			if(strcmp(mnt->mnt_type, "btrfs") != 0)
>  				continue;
>  
> +			printf("Testing if btrfs device is in the dev list: %s\n", mnt->mnt_fsname);
>  			ret = blk_file_in_dev_list(fs_devices_mnt, mnt->mnt_fsname);
>  		} else {
> +			printf("Testing if non-btrfs device is block or regular: %s\n", mnt->mnt_fsname);
>  			/* ignore entries in the mount table that are not
>  			   associated with a file*/
>  			if((ret = is_existing_blk_or_reg_file(mnt->mnt_fsname)) < 0)
> diff --git a/volumes.c b/volumes.c
> index 7671855..2496fbd 100644
> --- a/volumes.c
> +++ b/volumes.c
> @@ -130,6 +130,8 @@ static int device_list_add(const char *path,
>  		device->fs_devices = fs_devices;
>  	}
>  
> +	printf("Device added with name %s\n", device->name);
> +
>  	if (found_transid > fs_devices->latest_trans) {
>  		fs_devices->latest_devid = devid;
>  		fs_devices->latest_trans = found_transid;
> @@ -223,6 +225,7 @@ int btrfs_scan_one_device(int fd, const char *path,
>  		*total_devs = btrfs_super_num_devices(disk_super);
>  	uuid_unparse(disk_super->fsid, uuidbuf);
>  
> +	printf("Adding device %s to list\n", path);
>  	ret = device_list_add(path, disk_super, devid, fs_devices_ret);
>  
>  error_brelse:
> 
>