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From:   David Howells <dhowells@redhat.com>
In-Reply-To: <568749bd7cc02908ecf6f3d6a611b6f9cf5c4afd.camel@kernel.org>
References: <568749bd7cc02908ecf6f3d6a611b6f9cf5c4afd.camel@kernel.org> <164021479106.640689.17404516570194656552.stgit@warthog.procyon.org.uk> <164021543872.640689.14370017789605073222.stgit@warthog.procyon.org.uk>
To:     Jeff Layton <jlayton@kernel.org>
Cc:     dhowells@redhat.com, linux-cachefs@redhat.com,
        Trond Myklebust <trondmy@hammerspace.com>,
        Anna Schumaker <anna.schumaker@netapp.com>,
        Steve French <sfrench@samba.org>,
        Dominique Martinet <asmadeus@codewreck.org>,
        Matthew Wilcox <willy@infradead.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Omar Sandoval <osandov@osandov.com>,
        JeffleXu <jefflexu@linux.alibaba.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        linux-afs@lists.infradead.org, linux-nfs@vger.kernel.org,
        linux-cifs@vger.kernel.org, ceph-devel@vger.kernel.org,
        v9fs-developer@lists.sourceforge.net,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 40/68] cachefiles: Implement cache registration and withdrawal
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Date:   Thu, 06 Jan 2022 17:44:04 +0000
Message-ID: <2856724.1641491044@warthog.procyon.org.uk>
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Jeff Layton <jlayton@kernel.org> wrote:

> > +	/* check parameters */
> > +	ret = -EOPNOTSUPP;
> > +	if (d_is_negative(root) ||
> > +	    !d_backing_inode(root)->i_op->lookup ||
> > +	    !d_backing_inode(root)->i_op->mkdir ||
> > +	    !(d_backing_inode(root)->i_opflags & IOP_XATTR) ||
> > +	    !root->d_sb->s_op->statfs ||
> > +	    !root->d_sb->s_op->sync_fs ||
> > +	    root->d_sb->s_blocksize > PAGE_SIZE)
> > +		goto error_unsupported;
> > +
> 
> That's quite a collection of tests.
> 
> Most are obvious, but some comments explaining the need for others would
> not be a bad thing. In particular, why is s_blocksize > PAGE_SIZE
> unsupported?

It can't do page-sized DIO requests to a filesystem with a block size larger
than a page.  In the future I can work around that in conjunction with
netfslib by expanding read and write sizes.

> Also, should you vet whether the fs supports i_op->tmpfile here ?

That's a good idea.

David