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Date: Thu, 20 Aug 2015 11:00:20 -0400
From: Rich Felker <>
To: Sebastian Gottschall <>
Subject: Re: curious file access problem

On Thu, Aug 20, 2015 at 04:51:56PM +0200, Sebastian Gottschall wrote:
> Am 20.08.2015 um 15:48 schrieb Rich Felker:
> >On Thu, Aug 20, 2015 at 03:25:39PM +0200, Bastian Bittorf wrote:
> >>* Sebastian Gottschall <> [20.08.2015 13:21]:
> >>>>i cannot see this prob on openwrt.
> >>>>what is your arch and your exact musl version?
> >>>same es openwrt. but it seems to be related only to kernel 4.1 (or newer)
> >>>in 3.18 it does not happen in openwrt
> >>i can see it too - not on 3.18 but with kernel 4.1.5
> >>you are right, busybox 'route -n' is affected and does not
> >>see a default route (the same for hexdump, strings...)
> >In that case, it sounds like somebody broke the kernel. This is rather
> >unfortunate, and it would be great if someone could look into the bug
> >and get it fixed before these broken kernels are too widespread...
> there are some fib tree enhancements. i nailed it down to a patchset
> which i can apply and revert to let the problem show up
> the interesting thing is that uclibc doesnt show that behaviour. but
> i dont know why. maybe its some sort of application based routing
> table?

Again, if the bug is in the kernel's tracking of the pseudo-file
position state (which seems clear now), then whether it manifests or
not is almost certainly a matter of _how_ the reading takes place
(small chunks, big chunks, read vs readv vs pread, whether or not
seeking is involved, etc.). And this is going to vary between
applications, and if stdio is used by the application to perform the
reading, then it's also going to vary between stdio implementations
(and thus libcs).


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