On Wed, Aug 05, 2015 at 11:14:32AM -0700, Nicholas Miell wrote: > > > > On Aug 5, 2015, at 2:36 AM, Torvald Riegel <triegel@xxxxxxxxxx> wrote: > > > >> On Tue, 2015-08-04 at 11:50 -0700, Nicholas Miell wrote: > >>> On Aug 4, 2015, at 8:06 AM, Roland McGrath <roland@xxxxxxxxxxxxx> wrote: > >>> > >>> I think we are asserting that they are exactly that by dint of the confstr > >>> results for _CS_POSIX_V7_ILP32_OFF32_CFLAGS et al. So the question is what > >>> POSIX actually does or doesn't say about process-shared synchronization > >>> objects being shared between processes running programs built in different > >>> POSIX compilation environments. > >>> > >>> The other relevant question is whether 32/64 sharing of each particular > >>> pshared object has in fact worked reliably under glibc in the past. Since > >>> we haven't been clear and explicit about the subject before AFAIK, then if > >>> in fact it worked before then people might well have inferred that we made > >>> such an ABI guarantee. (I hope not, since if so we just broke it.) > >> > >> The relevant questions aren't what's the least useful behavior > >> that POSIX lets us get away with or can we leave it broken > >> because it never worked;'the questions are what do the other > >> operating systems do and what do the users want. > > > > Those are relevant questions, but they are not the only relevant ones. > > Some users would also like to share data structures between processes > > using different glibc builds (eg, different versions), and we won't > > promise that this works for obvioius reasons. > > The reasonable scenario is what we have right now -- 32 and 64-bit > versions of glibc built from the exact same git commit. And I'd > exclude static versions of glibc even if they're the same version. Why would you exclude static? IMO two static-linked executables using the same version of glibc should be compatible with each other even if you don't want to guarantee they'll be compatible with the same-version shared glibc. > > The semaphore example shows that there can be a disadvantage to > > guaranteeing 32/64b interoperability (specifically, the 64b code is more > > efficient). For mutex, I *currently* don't see a reason why we couldn't > > get away with just doing 32b stuff for the pshared case, but there's no > > guarantee that I can foresee all future needs either. > > > > Thus, if we would decide to guarantee 32/64b interoperability, we'd need > > to have at least strong use cases for that and a decent amount of > > confidence that making such a guarantee is unlikely to constrain the > > implementation in the future. > > Well, POSIX semaphores are supposed to be a replacement for System V > semaphores (and this extends to the rest of the POSIX IPC > primitives); right now they aren't. Only for some usage cases. As far as I can tell, POSIX semaphores are not intended to be required to be implemented as a kernel resource. They don't have permissions enforcement/safety against malicious processes, backout on async process termination, etc. Rich -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
