On 06/24/2016 12:12 AM, Fam Zheng wrote: > On Thu, 06/23 16:37, Eric Blake wrote: >> Improve the documentation of the write zeroes limits, to mention >> additional constraints that drivers should observe. Worth squashing >> into commit cf081fca, if that hadn't been pushed already :) >> >> Signed-off-by: Eric Blake <ebl...@redhat.com> >> >> --- >> v3: new patch, split off from "block: Switch discard length bounds..." >> --- >> include/block/block_int.h | 7 +++++-- >> 1 file changed, 5 insertions(+), 2 deletions(-) >> >> diff --git a/include/block/block_int.h b/include/block/block_int.h >> index 7d2b152..7a4a00f 100644 >> --- a/include/block/block_int.h >> +++ b/include/block/block_int.h >> @@ -331,11 +331,14 @@ typedef struct BlockLimits { >> int64_t discard_alignment; >> >> /* maximum number of bytes that can zeroized at once (since it is >> - * signed, it must be < 2G, if set) */ >> + * signed, it must be < 2G, if set), should be multiple of >> + * pwrite_zeroes_alignment. May be 0 if no inherent 32-bit limit */ > > "inherent 32-bit limit"? What is special about 32-bit other than this field is > 32-bit? Anyway, > > Reviewed-by: Fam Zheng <f...@redhat.com>
Someday, we may want to bump it up to a 64-bit field, and convert the driver callback for write_zeroes to take a 64-bit size. But first we'd have to audit to make sure all drivers properly advertise their maximum (for example, NBD is still hard-coded to a 32-bit maximum write_zeroes, even if the callback would permit a 64-bit size). -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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