Re: [PATCH] user_namespaces.7: Record new 340 line idmap limit

[Christian Brauner <christian.brauner-Z7WLFzj8eWMS+FvcfC7Uqw@public.gmane.org>]

[-- Attachment #1: Type: text/plain, Size: 1620 bytes --]

On Sun, Nov 19, 2017 at 10:00:39AM +0100, Michael Kerrisk (man-pages) wrote:
> Hello Christian,
> 
> 
> On 11/19/2017 02:25 AM, Christian Brauner wrote:
> > This patch documents the following commit:
> > 
> > commit 6397fac4915ab3002dc15aae751455da1a852f25
> > Author: Christian Brauner <christian.brauner-GeWIH/nMZzLQT0dZR+AlfA@public.gmane.org>
> > Date:   Wed Oct 25 00:04:41 2017 +0200
> > 
> >     userns: bump idmap limits to 340
> > 
> > Since Linux 4.15 the number of idmap lines has been bumped to 340.
> > The patch also removes the "(arbitrary)" in "There is an (arbitrary) limit on
> > the number of lines in the file." since the 340 line limit is well-explained by
> > the current implementation. The struct recording the idmaps is 12 bytes and
> > quite some proc files only allow writes the size of a single page size which is
> > 4096kB. This leaves room for 340 idmappings (340 * 12 = 4080 bytes).
> > The struct layout itself has been chosen very carefully to allow for an
> > implementation that limits the time-complexity for the idmap codepaths to
> > O(log n). However, I think it's unnecessary to expose this much implementation
> > detail to users in the man page. So only mention this in the commit message.
> > Furthermore, the comment about the page size restriction is misleading. The
> > kernel sources show that >= page size is considered an error.
> 
> Thanks for the patch and the detailed commit message.
> I've applied the patch, but restored the historical details,
> since users need also to now about older kernel behavior.

Thanks Michael!
Christian

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 801 bytes --]