Messages in this thread |  | | Date | Fri, 10 Apr 2015 14:01:32 -0400 | From | Jarod Wilson <> | Subject | Re: [PATCH try #3] proc: fix PAGE_SIZE limit of /proc/$PID/cmdline |
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On Fri, Apr 10, 2015 at 05:13:29PM +0300, Alexey Dobriyan wrote: > /proc/$PID/cmdline truncates output at PAGE_SIZE. It is easy to see with > > $ cat /proc/self/cmdline $(seq 1037) 2>/dev/null > > However, command line size was never limited to PAGE_SIZE but to 128 KB and > relatively recently limitation was removed altogether. > > People noticed and are asking questions: > http://stackoverflow.com/questions/199130/how-do-i-increase-the-proc-pid-cmdline-4096-byte-limit > > seq file interface is not OK, because it kmalloc's for whole output and > open + read(, 1) + sleep will pin arbitrary amounts of kernel memory. > To not do that, limit must be imposed which is incompatible with > arbitrary sized command lines. > > I apologize for hairy code, but this it direct consequence of command line > layout in memory and hacks to support things like "init [3]". > > The loops are "unrolled" otherwise it is either macros which hide > control flow or functions with 7-8 arguments with equal line count.
That definitely qualifies as hairy. How big of a problem is it really in practice if we continued using seq_file though? This only happens when someone actually accesses /proc/$PID/cmdline, no? And if they're doing that, they probably want that info, so is it so terrible if memory is held on to for a bit? We're only talking about a few kB. That said, properly walking the entire cmdline without having to specify an arbitrary limit ahead of time does sound slightly more end-user-friendly. I'll give this patch a spin here.
-- Jarod Wilson jarod@redhat.com
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