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

[Samuel Thibault]

Sergey Bugaev, le sam. 01 mai 2021 19:56:31 +0300, a ecrit:
> 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?

Tar itself, no.

> And in case of tarfs, the compression is handled by the store
> abstraction, which makes it transparent to the rest of the logic.

Ah, ok.
And in the zip case?

> > 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.

IIRC it isn't handled by the pager itself.

Samuel