On Thu, Apr 27, 2023 at 06:02:15PM +0100, Al Viro wrote: > On Thu, Apr 27, 2023 at 08:21:34AM -0700, Linus Torvalds wrote: > > On Thu, Apr 27, 2023 at 12:39 AM Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: > > > > > > int delayed_dup(struct file *file, unsigned flags) > > > > Ok, this is strange. Let me think about it. > > > > But even without thinking about it, this part I hate: > > > > > struct delayed_dup *p = kmalloc(sizeof(struct delayed_dup), GFP_KERNEL); > > > > Sure, if this is only used in unimportant code where performance > > doesn't matter, doing a kmalloc is fine. > > > > But if that is the only use, I think this is too subtle an interface. > > Still hadn't finished with the zoo... > > > Could we instead limit it to "we only have one pending delayed dup", > > and make this all be more like the restart-block thing, and be part of > > struct task_struct? > > Interesting... FWIW, *anything* that wants several descriptors has > special needs - there are some places like that (binder, for one) > and they have rather weird code implementing those. > > Just to restate the obvious: this is not applicable for the most frequent > caller - open(2). For the reasons that have nothing to do with performance. > If opening the file has hard-to-reverse side effects (like directory > modification due to O_CREAT), the things are very different. > > What I hope for is a small number of patterns, with clear rules for > choosing the one that is applicable and helpers for each that would > reduce the amount of headache when using it. And I've no problem > with "this particular pattern is not usable if you are adding more > than one descriptor" - that's not hard to understand and verify. > So I'm fine with doing that for one descriptor only and getting > rid of the allocation. > > BTW, another pattern is the same sans the "delayed" part. I.e. > "here's an opened file, get a descriptor and either attach the > file to it or fput() the damn thing; in any case, file reference > is consumed and descriptor-or-error is returned". That one is > definitely only for single descriptor case. > > In any case, I want to finish the survey of the callers first, just to > see what's there and whether anything is worth nicking. > > While we are at it, I want to make close_fd() use a very big red flag. > To the point of grepping for new callers in -next and asking the folks > who introduce those to explain WTF they are doing... Yeah, I'd fully support this and would be very nice to have.
