Group;
I can't argue with gcc on this one either:
drivers/scsi/sd.c: In function 'sd_read_capacity':
drivers/scsi/sd.c:1451: warning: comparison is always false due to limited range of data type
It reads to my eyes as if the function can never
select read_capacity_16 for very large devices.
Suggestions?
Mike
> I can't argue with gcc on this one either:
>
> drivers/scsi/sd.c: In function 'sd_read_capacity':
> drivers/scsi/sd.c:1451: warning: comparison is always false due to limited range of data type
>
> It reads to my eyes as if the function can never
> select read_capacity_16 for very large devices.
The code is:
if ((sizeof(sdkp->capacity) > 4) &&
(sdkp->capacity > 0xffffffffULL)) {
sdkp->capacity is a sector_t, and <linux/types.h> has:
#ifdef CONFIG_LBD
typedef u64 sector_t;
typedef u64 blkcnt_t;
#else
typedef unsigned long sector_t;
typedef unsigned long blkcnt_t;
#endif
so if you don't set CONFIG_LBD on a 32-bit architecture, then you are
correct that sd.c won't ever hit the READ_CAPACITY(16) case, and the
kernel won't be able to handle large SCSI disks.
On Fri June 5 2009, Roland Dreier wrote:
>
> > I can't argue with gcc on this one either:
> >
> > drivers/scsi/sd.c: In function 'sd_read_capacity':
> > drivers/scsi/sd.c:1451: warning: comparison is always false due to limited range of data type
> >
> > It reads to my eyes as if the function can never
> > select read_capacity_16 for very large devices.
>
> The code is:
>
> if ((sizeof(sdkp->capacity) > 4) &&
> (sdkp->capacity > 0xffffffffULL)) {
>
> sdkp->capacity is a sector_t, and <linux/types.h> has:
>
> #ifdef CONFIG_LBD
> typedef u64 sector_t;
> typedef u64 blkcnt_t;
> #else
> typedef unsigned long sector_t;
> typedef unsigned long blkcnt_t;
> #endif
>
> so if you don't set CONFIG_LBD on a 32-bit architecture, then you are
> correct that sd.c won't ever hit the READ_CAPACITY(16) case, and the
> kernel won't be able to handle large SCSI disks.
>
>
Perhaps then let gcc coherce the test value into a local sector_t holder
to make the warning go away (it would still be protected by the >4 thing).
Not a problem here - NetBooks don't (yet) come with that big a disk. ;)
Thanks
Mike