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Re: [Qemu-devel] Monitor file path length limitation
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] Monitor file path length limitation |
Date: |
Wed, 24 May 2017 10:26:58 -0500 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.0 |
On 05/24/2017 10:16 AM, Simon wrote:
> Hello,
>
> It seems that the monitor file path length is limited to about 100
> characters (107 to be precise).
Welcome to the joy of Unix socket (AF_UNIX) files. The kernel imposes a
hard length limit on sockaddr_un.sun_path[] (see 'man 7 unix') - and it
is indeed 107 characters plus a NUL terminator.
> -monitor
> 'unix:/home/user/vmtools/test/out/foobar.iso/foobar.iso_A/foobar.iso_B/foobar.iso_C/foobar.iso_D/foobar.iso_E/monitor.sock,server,nowait'
>
>
> With this command Qemu does not produce any warning or error message but
> create the socket file "mon" instead of the expected "monitor.sock".
Ideally, qemu should be telling you your path is too long to be created
as a unix socket, and failing up front, rather than silently truncating
and perhaps doing the wrong thing.
> Is there a clean way to work around this limitation?
Don't use longer path names than the kernel supports.
>
> As a side-note, is there any technical reason for such a limitation?
Yes, but you'll have to ask kernel folks for the reason.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
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