Re: [RFC PATCH tarfs 0/6] mmap support for tarfs

[Sergey Bugaev]

On Sat, May 1, 2021 at 7:38 PM Samuel Thibault <samuel.thibault@gnu.org> wrote:
> > on the other hand, the tar format, with its 512-byte
> > blocks, sounds very much like a filesystem image to me. isofs uses
> > diskfs, why doesn't tarfs?
>
> It's not exactly the same since you have compression in the way. But
> yes, that looks similar enough.

Does tar actually do any compression? I was under the impression that
tar is about just sticking multiple files together, and then you'd
apply gzip or bzip2 on top if you want compression. And in case of
tarfs, the compression is handled by the store abstraction, which
makes it transparent to the rest of the logic.

> Diskfs' pager_read_page does *not* have to lock the node, it just reads
> and returns the data. That's again a point where you see that having
> also the cache is in the way rather than helping.

Hmm, but doesn't the page reading/writing implementation need to
access the file size, atime/mtime, etc.? All of which may be changed
concurrently.

-- 
Sergey