Confused about SnapMapper::get_prefix

Commit Message

Ding Dinghua Feb. 4, 2015, 4:02 a.m. UTC

I think so, snap_id is defined and used as uint64_t in ceph, but here
static_cast may introduce bug, since two snap_id may get the same
prefix, then same key in snap_mapper.

> Should probably be cast to long unsigned with lX conversion specifier?
> -Sam
>
> On Tue, Feb 3, 2015 at 9:21 AM, Samuel Just <[e-mail]> wrote:
>> It looks like snapid_t is a uint64_t, but snprintf expects an unsigned there.
>> -Sam
>>
>> On Tue, Feb 3, 2015 at 9:15 AM, Gregory Farnum <[e-mail]> wrote:
>>> On Tue, Feb 3, 2015 at 4:12 AM, Ding Dinghua <[e-mail]> wrote:
>>>> Hi all:
>>>>       I don't understand why SnapMapper::get_prefix   static_cast snap
>>>> to unsigned:
>>>>
>>>> string SnapMapper::get_prefix(snapid_t snap)
>>>> {
>>>>   char buf[100];
>>>>   int len = snprintf(
>>>>     buf, sizeof(buf),
>>>>     "%.*X_", (int)(sizeof(snap)*2),
>>>>     static_cast<unsigned>(snap));
>>>>   return MAPPING_PREFIX + string(buf, len);
>>>> }
>>>>
>>>> Will this limit snapshot count in pool to 2^32 -1 ?
>>>>
>>>> Could anyone clarify ? Thanks
>>>
>>> I think the code base is a little confused about whether snaps should
>>> be 32 or 64 bits in various places. :( That said, the size of unsigned
>>> can vary across architectures, so this should probably be sized more
>>> explicitly as whatever it's supposed to be on the disk...

Patch

diff --git a/src/osd/SnapMapper.cc b/src/osd/SnapMapper.cc
index 315e2e2..27cc2b7 100644
--- a/src/osd/SnapMapper.cc
+++ b/src/osd/SnapMapper.cc
@@ -72,8 +72,7 @@  string SnapMapper::get_prefix(snapid_
t snap)
   char buf[100];
   int len = snprintf(
     buf, sizeof(buf),
-    "%.*X_", (int)(sizeof(snap)*2),
-    static_cast<unsigned>(snap));
+    "%.*llX_", (int)(sizeof(snap)*2), snap);

2015-02-04 1:25 GMT+08:00 Samuel Just <[e-mail]>: