linux-kernel - Re: [PATCH v6 01/30] iov_iter: Add ITER

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Message-ID: <YG+s0iw5o91KQIlW@zeniv-ca.linux.org.uk>
Date:   Fri, 9 Apr 2021 01:24:34 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     David Howells <dhowells@...hat.com>
Cc:     linux-fsdevel@...r.kernel.org,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Christoph Hellwig <hch@....de>, linux-mm@...ck.org,
        linux-cachefs@...hat.com, linux-afs@...ts.infradead.org,
        linux-nfs@...r.kernel.org, linux-cifs@...r.kernel.org,
        ceph-devel@...r.kernel.org, v9fs-developer@...ts.sourceforge.net,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        Steve French <sfrench@...ba.org>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Jeff Layton <jlayton@...hat.com>,
        David Wysochanski <dwysocha@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 01/30] iov_iter: Add ITER_XARRAY

On Thu, Apr 08, 2021 at 03:04:07PM +0100, David Howells wrote:
> Add an iterator, ITER_XARRAY, that walks through a set of pages attached to
> an xarray, starting at a given page and offset and walking for the
> specified amount of bytes.  The iterator supports transparent huge pages.
> 
> The iterate_xarray() macro calls the helper function with rcu_access()
> helped.  I think that this is only a problem for iov_iter_for_each_range()
> - and that returns an error for ITER_XARRAY (also, this function does not
> appear to be called).

Unused since lustre had gone away.

> +#define iterate_all_kinds(i, n, v, I, B, K, X) {		\

Do you have any users that would pass different B and X?

> @@ -1440,7 +1665,7 @@ ssize_t iov_iter_get_pages_alloc(struct iov_iter *i,
>  		return v.bv_len;
>  	}),({
>  		return -EFAULT;
> -	})
> +	}), 0

Correction - users that might get that flavour.  This one explicitly checks
for xarray and doesn't get to iterate_... in that case.