[Xen-devel] blktap2 header consistency between userspace and kernel space

[Sylvain Munaut <s.munaut@xxxxxxxxxxxxxxxxxxxx>]

Hi,


I'm wondering what's up with the blktap device info structure in blktap2.

Here's the one from the blktap2 userspace utilities:
(it's the same in debian package source, xen git tree and the github
blktap2 repo)

struct blktap_device_info {
        unsigned long long      capacity;
        unsigned int            sector_size;
        unsigned int            physical_sector_size;
        unsigned long           flags;
        unsigned long           __rsvd[4];
};


And this is the one in the kernel :
(as found on the debian dkms or some blktap patch for kernel 3.2)

struct blktap_device_info {
        unsigned long long      capacity;
        unsigned int            sector_size;
        unsigned long           flags;
        unsigned int            phys_block_size;
        unsigned int            phys_block_offset;
        unsigned int            trim_block_size;
        unsigned int            trim_block_offset;
};


Now the fields phys_XXX and trim_XXX won't be accessed by the kernel
until it find the appropriate flag.

But the position of the 'flags' field is not the same AFAICT !  I'm
under 64bits, so it just happen to work because the 'unsigned long
flags' will be 64 bits aligned leaving a hole after sector_size in the
kernel structure, but on 32 bits arch, I think it'll start using
'physical_sector_size' as the flag field.

Am I missing something here ?


Cheers,

    Sylvain

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