udf: allow implicit blocksize specification during mount

Hi! I found that following UDF patch was included into linus tree:
https://patchwork.kernel.org/patch/9524557/

It is really a good improvement to recognize UDF file system which have block size different from disk sector size and also different from 2048.

But should not detection on 4K native disks (4096/4096) try to also use block size of 512 bytes? Because current loop is from logical sector size to 4096.

Anyway, macro UDF_DEFAULT_BLOCKSIZE is not used in udf source code anymore, so it can be deleted. I think its name was incorrect as default block size for UDF should be logical block size of disk, not hardcoded value 2048 which is logical block size for optical media.

Hi,

Quoted 7 lines · Pali Rohár

Hi! I found that following UDF patch was included into linus tree:
https://patchwork.kernel.org/patch/9524557/

It is really a good improvement to recognize UDF file system which have block size different from disk sector size and also different from 2048.

Quoted 3 lines

But should not detection on 4K native disks (4096/4096) try to also use block size of 512 bytes? Because current loop is from logical sector size to 4096.

By definition, bdev_logical_block_size() is the smallest block size a device can support. So if it is larger than 512, the device driver had explicitely declared that it cannot handle smaller blocks...

Look at the comment before "blk_queue_logical_block_size":

/**
* blk_queue_logical_block_size - set logical block size for the
queue * @q: the request queue for the device
* @size: the logical block size, in bytes
*
* Description:

 *   This should be set to the lowest possible block size that the
 *   storage device can address.  The default of 512 covers most
 *   hardware.

**/

Quoted 5 lines

Anyway, macro UDF_DEFAULT_BLOCKSIZE is not used in udf source code anymore, so it can be deleted. I think its name was incorrect as default block size for UDF should be logical block size of disk, not hardcoded value 2048 which is logical block size for optical media.

Thanks. Removed.

Honza

Quoted 10 lines · On Tuesday 13 June 2017 14:59:55 Jan Kara wrote:

Hi,

Quoted 7 lines · Pali Roh�r

Hi! I found that following UDF patch was included into linus tree:
https://patchwork.kernel.org/patch/9524557/

It is really a good improvement to recognize UDF file system which have block size different from disk sector size and also different from 2048.

Quoted 7 lines

Quoted 3 lines

But should not detection on 4K native disks (4096/4096) try to also use block size of 512 bytes? Because current loop is from logical sector size to 4096.

By definition, bdev_logical_block_size() is the smallest block size a device can support. So if it is larger than 512, the device driver had explicitely declared that it cannot handle smaller blocks...

Ok, but it is a really problem when trying to read data from filesystem which has smaller blocks as the smallest block size of a device?

In the worst case filesystem driver needs to read 512 bytes, but device can send only block of 4096 bytes (as it does not support smaller block). Driver receives 4096 bytes, then it process just first 512 bytes and do not care about remaining data...

Quoted 22 lines · Pali Rohár

Quoted 10 lines · On Tuesday 13 June 2017 14:59:55 Jan Kara wrote:

Hi,

Quoted 7 lines · Pali Rohár

Hi! I found that following UDF patch was included into linus tree:
https://patchwork.kernel.org/patch/9524557/

It is really a good improvement to recognize UDF file system which have block size different from disk sector size and also different from 2048.

Quoted 7 lines

Quoted 3 lines

But should not detection on 4K native disks (4096/4096) try to also use block size of 512 bytes? Because current loop is from logical sector size to 4096.

By definition, bdev_logical_block_size() is the smallest block size a device can support. So if it is larger than 512, the device driver had explicitely declared that it cannot handle smaller blocks...

Ok, but it is a really problem when trying to read data from filesystem which has smaller blocks as the smallest block size of a device?

Quoted 4 lines

In the worst case filesystem driver needs to read 512 bytes, but device can send only block of 4096 bytes (as it does not support smaller block). Driver receives 4096 bytes, then it process just first 512 bytes and do not care about remaining data...

Well, as much as I agree this is possible in principle, the block layer, block device page cache etc. don't handle this so it would be a non-trivial effort to support this.