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SubjectRe: [PATCH v2 0/5] pid: add pidfd_open()
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> On Mar 31, 2019, at 3:17 PM, Linus Torvalds <torvalds@linux-foundation.org> wrote:
>
>> On Sun, Mar 31, 2019 at 2:10 PM Christian Brauner <christian@brauner.io> wrote:
>>
>> I don't think that we want or can make them equivalent since that would
>> mean we depend on procfs.
>
> Sure we can.
>
> If /proc is enabled, then you always do that dance YOU ALREADY WROTE
> THE CODE FOR to do the stupid ioctl.
>
> And if /procfs isn't enabled, then you don't do that.
>
> Ta-daa. Done. No stupid ioctl, and now /proc and pidfd_open() return
> the same damn thing.
>
> And guess what? If /proc isn't enabled, then obviously pidfd_open()
> gives you the /proc-less thing, but at least there is no crazy "two
> different file descriptors for the same thing" situation, because then
> the /proc one doesn't exist.
>

I wish we could do this, and, in a clean design, it would be a no-brainer. But /proc has too much baggage. Just to mention two such things, there’s “net” and “../sys”. This crud is why we have all kinds of crazy rules that prevent programs in sandboxes from making a new mounts and mounting /proc in it. If we make it possible to clone a new process and this access /proc without having /proc mounted, we’ll open up a big can of worms.

Maybe we could have a sanitized view of /proc and make a pidfd be a directory fd pointing at that.
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