Re: [PATCH 10/18] libxfs: introduce libxfs_buf_read_uncached

Darrick J. Wong
2020-02-21T20:50:36Z

On Fri, Feb 21, 2020 at 06:48:33AM -0800, Christoph Hellwig wrote:
> On Wed, Feb 19, 2020 at 05:43:37PM -0800, Darrick J. Wong wrote:
> > From: Darrick J. Wong <darrick.wong@oracle.com>
> >
> > Introduce an uncached read function so that userspace can handle them in
> > the same way as the kernel. This also eliminates the need for some of
> > the libxfs_purgebuf calls (and two trips into the cache code).
> >
> > Refactor the get/read uncached buffer functions to hide the details of
> > uncached buffer-ism in rdwr.c.
>
> Split this into one patch adding the functionality to libxfs and
> one each to convert db and copy over with a good rationale for the
> switch in each case?

Both programs use the uncached read for the same purpose, which is to
read the superblock without polluting the buffer cache when we haven't
yet established the filesystem sector size.

The only reason why repair doesn't need patching is that reaches into
the buffer cache internals to call lseek and read by hand. I guess that
should be fixed, separately.

--D