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Date: Mon, 8 Aug 2011 17:48:42 +0200
From: Tejun Heo <tj@kernel.org>
To: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Nathan Lynch <ntl@pobox.com>, Oren Laadan <orenl@cs.columbia.edu>,
        Daniel Lezcano <dlezcano@fr.ibm.com>, Serge Hallyn <serue@us.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Glauber Costa <glommer@parallels.com>, containers@lists.osdl.org,
        linux-kernel@vger.kernel.org, Pavel Emelyanov <xemul@parallels.com>,
        Serge Hallyn <serge.hallyn@canonical.com>
Subject: Re: [patch 1/4] proc: Introduce the /proc/<pid>/mfd/ directory
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References: <20110807210112.245578619@openvz.org>
 <20110807210526.741513583@openvz.org>
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Hello,

Maybe cc'ing linux-mm is a good idea for this one?

On Mon, Aug 08, 2011 at 01:01:13AM +0400, Cyrill Gorcunov wrote:
> This one behaves similarly to the /proc/<pid>/fd/ one - it contains symlinks
> one for each mapping with file, the name of a symlink is vma->vm_start, the
> target is the file. Opening a symlink results in a file that point exactly
> to the same inode as them vma's one.
> 
> This thing is aimed to help checkpointing processes.

I generally agree this is a good idea.  Can you please add how it
would look (say, example ls -l output) in the patch description?
Maybe some people think using both start and end addresses for symlink
name is better?

Another nit: I find the 'mfd' name a bit confusing as there's no file
descriptor involved at all.  Maybe map_files (as we already have maps)
or something like that?

> +static int proc_mfd_get_link(struct inode *inode, struct path *path)
...
> +	down_read(&mm->mmap_sem);
> +	for (vma = mm->mmap; vma; vma = vma->vm_next) {
> +		if (vma->vm_start < vm_start)
> +			continue;
> +		if (vma->vm_start > vm_start)
> +			break;

Why do linear walk instead of find_vma()?

> +static const struct dentry_operations tid_mfd_dentry_operations = {
> +	.d_delete	= pid_delete_dentry,
> +};

Don't we also need revalidation here like tid_fd_dentry_operations?
Also, I think it would be better if all the related functions are
collected into one contiguous chunk.  The scattering doesn't seem to
make much sense.

> +static struct dentry *proc_mfd_lookup(struct inode *dir,
> +		struct dentry *dentry, struct nameidata *nd)
> +{
..
> +	down_read(&mm->mmap_sem);
> +	for (vma = mm->mmap; vma; vma = vma->vm_next) {
> +		if (vma->vm_start == vm_start)
> +			break;
> +		if (vma->vm_start > vm_start)
> +			goto out_no_vma;
> +	}

Ditto, no reason to do linear walk.

Thanks.

-- 
tejun