Re: [PATCH] fuse: Add support for fuse stacked I/O

On Fri, Jan 15, 2016 at 1:43 PM, Linus Torvalds
[off-list ref] wrote:

On Fri, Jan 15, 2016 at 11:29 AM, Nikhilesh Reddy [off-list ref] wrote:

quoted

FUSE allows users to implement extensions to filesystems ..such as enforcing policy or permissions without having to modify the kernel or maintain the policy in the kernel.

One such example is what was quoted by Antonio above ..
Another example is a fuse based filesystem that tries to enforce additional permissions on a FAT based mount point.

From what i could google there are many FUSE based filesystems out there that do things during the open call but simply pass through the read/and write I/O calls to the local "lower" filesystem where they actually store the data.

So I think these are valid use-cases, and I just think that they should

 (a) be documented in the commit message as explanations of why people
would do this/

 (b) not be called "stacked", because that tends to have some other
connotations to fs people.

I don't know what a better term would be, but you yourself used "pass
through". Maybe that (perhaps together with a clarification that it's
a per-file thing) might work fine.

Btw, why is mmap not passed through? That sounds fairly simple and
straightforward, I'm not seeing why it would be missing.

If mmap sets vm_file to the underlying thing, wouldn't CRIU and
anything else that uses map_files get confused?  Or did you have
something else in mind?

--Andy