netfs: Pass more information on how to deal with a hole in the cache

Pass more information to the cache on how to deal with a hole if it
encounters one when trying to read from the cache.  Three options are
provided:

 (1) NETFS_READ_HOLE_IGNORE.  Read the hole along with the data, assuming
     it to be a punched-out extent by the backing filesystem.

 (2) NETFS_READ_HOLE_CLEAR.  If there's a hole, erase the requested region
     of the cache and clear the read buffer.

 (3) NETFS_READ_HOLE_FAIL.  Fail the read if a hole is detected.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819612321.215744.9738308885948264476.stgit@warthog.procyon.org.uk/
Link: https://lore.kernel.org/r/163906914460.143852.6284247083607910189.stgit@warthog.procyon.org.uk/
Link: https://lore.kernel.org/r/163967119923.1823006.15637375885194297582.stgit@warthog.procyon.org.uk/
Link: https://lore.kernel.org/r/164021519762.640689.16994364383313159319.stgit@warthog.procyon.org.uk/

diff --git a/fs/netfs/read_helper.c b/fs/netfs/read_helper.c
index 9dd76b8..6169659 100644 (file)
--- a/fs/netfs/read_helper.c
+++ b/fs/netfs/read_helper.c
@@ -170,7 +170,7 @@ static void netfs_cache_read_terminated(void *priv, ssize_t transferred_or_error
  */
 static void netfs_read_from_cache(struct netfs_read_request *rreq,
                                  struct netfs_read_subrequest *subreq,
-                                 bool seek_data)
+                                 enum netfs_read_from_hole read_hole)
 {
        struct netfs_cache_resources *cres = &rreq->cache_resources;
        struct iov_iter iter;
@@ -180,7 +180,7 @@ static void netfs_read_from_cache(struct netfs_read_request *rreq,
                        subreq->start + subreq->transferred,
                        subreq->len   - subreq->transferred);
 
-       cres->ops->read(cres, subreq->start, &iter, seek_data,
+       cres->ops->read(cres, subreq->start, &iter, read_hole,
                        netfs_cache_read_terminated, subreq);
 }
 
@@ -461,7 +461,7 @@ static void netfs_rreq_short_read(struct netfs_read_request *rreq,
        netfs_get_read_subrequest(subreq);
        atomic_inc(&rreq->nr_rd_ops);
        if (subreq->source == NETFS_READ_FROM_CACHE)
-               netfs_read_from_cache(rreq, subreq, true);
+               netfs_read_from_cache(rreq, subreq, NETFS_READ_HOLE_CLEAR);
        else
                netfs_read_from_server(rreq, subreq);
 }
@@ -789,7 +789,7 @@ static bool netfs_rreq_submit_slice(struct netfs_read_request *rreq,
                netfs_read_from_server(rreq, subreq);
                break;
        case NETFS_READ_FROM_CACHE:
-               netfs_read_from_cache(rreq, subreq, false);
+               netfs_read_from_cache(rreq, subreq, NETFS_READ_HOLE_IGNORE);
                break;
        default:
                BUG();

diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index 5a46fde..b46c39d 100644 (file)
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -197,6 +197,15 @@ struct netfs_read_request_ops {
 };
 
 /*
+ * How to handle reading from a hole.
+ */
+enum netfs_read_from_hole {
+       NETFS_READ_HOLE_IGNORE,
+       NETFS_READ_HOLE_CLEAR,
+       NETFS_READ_HOLE_FAIL,
+};
+
+/*
  * Table of operations for access to a cache.  This is obtained by
  * rreq->ops->begin_cache_operation().
  */
@@ -208,7 +217,7 @@ struct netfs_cache_ops {
        int (*read)(struct netfs_cache_resources *cres,
                    loff_t start_pos,
                    struct iov_iter *iter,
-                   bool seek_data,
+                   enum netfs_read_from_hole read_hole,
                    netfs_io_terminated_t term_func,
                    void *term_func_priv);