false physical blocksize detected about go-diskfs HOT 4 CLOSED

The sector sizes are determined here. If you dig in, you can see that it determines the device type (correctly, a block device, when you give it /dev/sr0), and then it calls getSectorSizes (I linked to the Unix one, since, as far as I can tell, you are running on a Unix-like system):

func getSectorSizes(f *os.File) (int64, int64, error) {
	fd := f.Fd()
	logicalSectorSize, err := unix.IoctlGetInt(int(fd), blksszGet)
	if err != nil {
		return 0, 0, fmt.Errorf("Unable to get device logical sector size: %v", err)
	}
	physicalSectorSize, err := unix.IoctlGetInt(int(fd), blkbszGet)
	if err != nil {
		return 0, 0, fmt.Errorf("Unable to get device physical sector size: %v", err)
	}
	return int64(logicalSectorSize), int64(physicalSectorSize), nil
}

I find it interesting that fdisk returned a different value than the ioctl calls, as I think that fdisk does those ioctl calls. It is worth looking into their source code.

The source for fdisk listing (fdisk -l) is here

from go-diskfs.

Yup, code starts here:

/*
 * Get physical block device size. The BLKPBSZGET is supported since Linux
 * 2.6.32. For old kernels is probably the best to assume that physical sector
 * size is the same as logical sector size.
 *
 * Example:
 *
 * rc = blkdev_get_physector_size(fd, &physec);
 * if (rc || physec == 0) {
 *	rc = blkdev_get_sector_size(fd, &physec);
 *	if (rc)
 *		physec = DEFAULT_SECTOR_SIZE;
 * }
 */
#ifdef BLKPBSZGET
int blkdev_get_physector_size(int fd, int *sector_size)
{
	if (ioctl(fd, BLKPBSZGET, &sector_size) >= 0)
		return 0;
	return -1;
}
#else
int blkdev_get_physector_size(int fd __attribute__((__unused__)), int *sector_size)
{
	*sector_size = DEFAULT_SECTOR_SIZE;
	return 0;
}
#endif

And the definitions here:

/* block device topology ioctls, introduced in 2.6.32 (commit ac481c20) */
# ifndef BLKIOMIN
#  define BLKIOMIN   _IO(0x12,120)
#  define BLKIOOPT   _IO(0x12,121)
#  define BLKALIGNOFF _IO(0x12,122)
#  define BLKPBSZGET _IO(0x12,123)
# endif

I wonder if it is being misset on different platforms, because we have it fixed here:

	blkbszGet                        = 0x80081270

It is possible, especially in a virtualized environment (I saw you are running in qemu).

Hmm, oh hold on. Even with a fixed number, I am seeing it as we set it to the value of BLKBSZGET and not BLKPBSZGET, which are different values.

Let's start with a branch that sets it to the "right" fixed value for now, then let's see about getting it dynamically determined.

from go-diskfs.

@mraerino can you try against this branch and see what you get? https://github.com/diskfs/go-diskfs/tree/pbsize

from go-diskfs.

works! #107 (review)

from go-diskfs.