Re: [patch 1/4] proc: Introduce the /proc/<pid>/mfd/ directory

From: Tejun Heo
Date: Mon Aug 08 2011 - 11:48:51 EST


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.


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