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    SubjectRe: [RFC PATCH 02/12] netfs: Add an iov_iter to the read subreq for the network fs/cache to use
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    On Wed, 2021-07-21 at 14:44 +0100, David Howells wrote:
    > Add an iov_iter to the read subrequest and set it up to define the
    > destination buffer to write into. This will allow future patches to point
    > to a bounce buffer instead for purposes of handling oversize writes,
    > decryption (where we want to save the encrypted data to the cache) and
    > decompression.
    >
    > Signed-off-by: David Howells <dhowells@redhat.com>
    > ---
    >
    > fs/afs/file.c | 6 +-----
    > fs/netfs/read_helper.c | 5 ++++-
    > include/linux/netfs.h | 2 ++
    > 3 files changed, 7 insertions(+), 6 deletions(-)
    >
    > diff --git a/fs/afs/file.c b/fs/afs/file.c
    > index c9c21ad0e7c9..ca529f23515a 100644
    > --- a/fs/afs/file.c
    > +++ b/fs/afs/file.c
    > @@ -319,11 +319,7 @@ static void afs_req_issue_op(struct netfs_read_subrequest *subreq)
    > fsreq->len = subreq->len - subreq->transferred;
    > fsreq->key = subreq->rreq->netfs_priv;
    > fsreq->vnode = vnode;
    > - fsreq->iter = &fsreq->def_iter;
    > -
    > - iov_iter_xarray(&fsreq->def_iter, READ,
    > - &fsreq->vnode->vfs_inode.i_mapping->i_pages,
    > - fsreq->pos, fsreq->len);
    > + fsreq->iter = &subreq->iter;
    >
    > afs_fetch_data(fsreq->vnode, fsreq);
    > }
    > diff --git a/fs/netfs/read_helper.c b/fs/netfs/read_helper.c
    > index 0b6cd3b8734c..715f3e9c380d 100644
    > --- a/fs/netfs/read_helper.c
    > +++ b/fs/netfs/read_helper.c
    > @@ -150,7 +150,7 @@ static void netfs_clear_unread(struct netfs_read_subrequest *subreq)
    > {
    > struct iov_iter iter;
    >
    > - iov_iter_xarray(&iter, WRITE, &subreq->rreq->mapping->i_pages,
    > + iov_iter_xarray(&iter, READ, &subreq->rreq->mapping->i_pages,

    What's up with the WRITE -> READ change here? Was that a preexisting
    bug?

    > subreq->start + subreq->transferred,
    > subreq->len - subreq->transferred);
    > iov_iter_zero(iov_iter_count(&iter), &iter);
    > @@ -745,6 +745,9 @@ netfs_rreq_prepare_read(struct netfs_read_request *rreq,
    > if (WARN_ON(subreq->len == 0))
    > source = NETFS_INVALID_READ;
    >
    > + iov_iter_xarray(&subreq->iter, READ, &rreq->mapping->i_pages,
    > + subreq->start, subreq->len);
    > +
    > out:
    > subreq->source = source;
    > trace_netfs_sreq(subreq, netfs_sreq_trace_prepare);
    > diff --git a/include/linux/netfs.h b/include/linux/netfs.h
    > index fe9887768292..5e4fafcc9480 100644
    > --- a/include/linux/netfs.h
    > +++ b/include/linux/netfs.h
    > @@ -17,6 +17,7 @@
    > #include <linux/workqueue.h>
    > #include <linux/fs.h>
    > #include <linux/pagemap.h>
    > +#include <linux/uio.h>
    >
    > /*
    > * Overload PG_private_2 to give us PG_fscache - this is used to indicate that
    > @@ -112,6 +113,7 @@ struct netfs_cache_resources {
    > struct netfs_read_subrequest {
    > struct netfs_read_request *rreq; /* Supervising read request */
    > struct list_head rreq_link; /* Link in rreq->subrequests */
    > + struct iov_iter iter; /* Iterator for this subrequest */
    > loff_t start; /* Where to start the I/O */
    > size_t len; /* Size of the I/O */
    > size_t transferred; /* Amount of data transferred */
    >
    >

    --
    Jeff Layton <jlayton@redhat.com>

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