On Tue, Mar 3, 2015 at 4:53 PM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: > On Tue, Mar 03, 2015 at 04:37:00PM -0800, Dan Ehrenberg wrote: >> Previously, stat on 32-bit platforms used old-style encoding and >> validation of major-minor pairs, with 8:8 bits. However, dev_t is >> 32-bits on these platforms, and coreutils seems to be treating the >> values as 12:20 new-style values. The only reason to use the old >> version is in the implementation of a legacy filesystem format which >> only has 16 bits of space. Communicating a 12:20 value to userspace >> when sizeof dev_t == 4 can be done on either a 32-bit or 64-bit >> platform. >> >> This patch removes the artificial restriction in major:minor size. >> The only backwards incompatibility which results is sometimes stat >> succeeds if -EOVERFLOW would be returned otherwise. The legacy >> old-style stat call is retained as-is. > > Umm... You do realize that coreutils are _very_ far from being the only > userland programs handling the data returned by stat(2), right? > > What's to guarantee that your ABI change won't break any of those? I guess it's impossible to guarantee, but if there is an error, it'll be that an -EOVERFLOW error is suppressed and the high bits of the major:minor pair are shaved off by the userspace program. I would suspect that this would just make debugging harder, rather than actually break an automated program which counts on getting EOVERFLOW from a huge block device, but no way to know. The block device has to actually exist for this to happen, and all we're talking about is stat failing. So it's replacing an an error code with erroneous way to get data about a device node (erroneous just because userspace ignores some of the bits with the answer). How about this instead: a new config option to switch on the 12:20 major:minor numbers on 32-bit platforms? Dan -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
