Re: [patch 12/12] fuse: add blksize field to fuse_attr

Miklos Szeredi
2007-10-04T23:15:30Z

> > From: Miklos Szeredi <mszeredi@suse.cz>
> >
> > Allow the userspace filesystem to supply a blksize value to be
> > returned by stat() and friends. If the field is zero, it defaults to
> > the old PAGE_CACHE_SIZE value.
> >
>
> Why does fuse need this feature?

There are cases, when the filesystem will be passed the buffer from a
single read or write call, namely:

1) in 'direct-io' mode (not O_DIRECT), read/write requests don't go
through the page cache, but go directly to the userspace fs

2) currently buffered writes are done with single page requests, but
if Nick's ->perform_write() patch goes it, it will be possible to
do larger write requests. But only if the original write() was
also bigger than a page.

In these cases the filesystem might want to give a hint to the app
about the optimal I/O size.

Miklos