Re: [PATCH v4 2/2] tools/xenstore: set open file descriptor limit for xenstored

[Juergen Gross <jgross@xxxxxxxx>]

On 27.09.21 16:40, Andrew Cooper wrote:
> On 27/09/2021 15:24, Juergen Gross wrote:
> > On 27.09.21 16:13, Andrew Cooper wrote:
> > > On 27/09/2021 11:48, Juergen Gross wrote:
> > > > Add a configuration item for the maximum number of open file
> > > > descriptors xenstored should be allowed to have.
> > > >
> > > > The default should be "unlimited" in order not to restrict xenstored
> > > > in the number of domains it can support, but unfortunately the prlimit
> > > > command requires specification of a real value for the number of files,
> > > > so use 262144 as the default value.
> > > Citation needed.
> > >
> > > prlimit -nunlimited
> > >
> > > prlimit --nofile=unlimited
> > >
> > > both work fine, and strace confirms they issue correct system calls.
> > Not on my test system:
> >
> > # prlimit --pid 734 --nofile=unlimited
> > prlimit: failed to set the NOFILE resource limit: Operation not permitted
> > # prlimit --pid 734 --nofile=262144
> > #
> What does strace say in both of these cases?
prlimit64(734, RLIMIT_NOFILE, {rlim_cur=RLIM64_INFINITY, 
rlim_max=RLIM64_INFINITY}, NULL) = -1 EPERM (Operation not permitted)
write(2, "prlimit: ", 9prlimit: )                = 9

vs.

prlimit64(734, RLIMIT_NOFILE, {rlim_cur=256*1024, rlim_max=256*1024}, 
NULL) = 0
> > > Support for "unlimited" as a parameter has existed for the entire
> > > lifetime of the utility,
> > > https://github.com/karelzak/util-linux/commit/6bac2825af7216c5471148e219dbcf62ec5ede84
> > Yes, but not all systems seem to support raising the limit to
> > "unlimited".
> That's as maybe, but
>
> prlimit64(0, RLIMIT_NOFILE, {rlim_cur=RLIM64_INFINITY,
> rlim_max=RLIM64_INFINITY}, NULL) = -1 EPERM (Operation not permitted)
>
> is a Linux issue, not a prlimit bug.
Nevertheless it isn't a good idea to use this setting in case it isn't
supported in all Linux distros/versions we care about.


Juergen

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