[PATCH 1/2] fscache,cachefiles: add prepare_ondemand_read() callback

[Jingbo Xu]

Add prepare_ondemand_read() callback dedicated for the on-demand read
scenario, so that callers from this scenario can be decoupled from
netfs_io_subrequest.

To reuse the hole detecting logic as mush as possible, both the
implementation of prepare_read() and prepare_ondemand_read() inside
Cachefiles call a common routine.

In the near future, prepare_read() will get enhanced and more
information will be needed and then returned to callers. Thus
netfs_io_subrequest is a reasonable candidate for holding places for all
these information needed in the internal implementation.

Signed-off-by: Jingbo Xu <jefflexu@xxxxxxxxxxxxxxxxx>
---
 fs/cachefiles/io.c                | 42 +++++++++++++++++++++++++------
 include/linux/netfs.h             |  7 ++++++
 include/trace/events/cachefiles.h |  4 +--
 3 files changed, 43 insertions(+), 10 deletions(-)

diff --git a/fs/cachefiles/io.c b/fs/cachefiles/io.c
index 000a28f46e59..6427259fcba9 100644
--- a/fs/cachefiles/io.c
+++ b/fs/cachefiles/io.c
@@ -385,16 +385,11 @@ static int cachefiles_write(struct netfs_cache_resources *cres,
 				  term_func, term_func_priv);
 }
 
-/*
- * Prepare a read operation, shortening it to a cached/uncached
- * boundary as appropriate.
- */
-static enum netfs_io_source cachefiles_prepare_read(struct netfs_io_subrequest *subreq,
-						      loff_t i_size)
+static enum netfs_io_source cachefiles_do_prepare_read(struct netfs_io_subrequest *subreq,
+						       struct netfs_cache_resources *cres,
+						       loff_t i_size)
 {
 	enum cachefiles_prepare_read_trace why;
-	struct netfs_io_request *rreq = subreq->rreq;
-	struct netfs_cache_resources *cres = &rreq->cache_resources;
 	struct cachefiles_object *object;
 	struct cachefiles_cache *cache;
 	struct fscache_cookie *cookie = fscache_cres_cookie(cres);
@@ -501,6 +496,36 @@ static enum netfs_io_source cachefiles_prepare_read(struct netfs_io_subrequest *
 	return ret;
 }
 
+/*
+ * Prepare a read operation, shortening it to a cached/uncached
+ * boundary as appropriate.
+ */
+static enum netfs_io_source cachefiles_prepare_read(struct netfs_io_subrequest *subreq,
+						      loff_t i_size)
+{
+	return cachefiles_do_prepare_read(subreq,
+			&subreq->rreq->cache_resources, i_size);
+}
+
+/*
+ * Prepare an on-demand read operation, shortening it to a cached/uncached
+ * boundary as appropriate.
+ */
+static enum netfs_io_source cachefiles_prepare_ondemand_read(struct netfs_cache_resources *cres,
+		loff_t start, size_t *_len, loff_t i_size)
+{
+	enum netfs_io_source source;
+	struct netfs_io_subrequest subreq = {
+		.start	= start,
+		.len	= *_len,
+		.flags	= 1 << NETFS_SREQ_ONDEMAND,
+	};
+
+	source = cachefiles_do_prepare_read(&subreq, cres, i_size);
+	*_len = subreq.len;
+	return source;
+}
+
 /*
  * Prepare for a write to occur.
  */
@@ -621,6 +646,7 @@ static const struct netfs_cache_ops cachefiles_netfs_cache_ops = {
 	.write			= cachefiles_write,
 	.prepare_read		= cachefiles_prepare_read,
 	.prepare_write		= cachefiles_prepare_write,
+	.prepare_ondemand_read	= cachefiles_prepare_ondemand_read,
 	.query_occupancy	= cachefiles_query_occupancy,
 };
 
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index f2402ddeafbf..d82071c37133 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -267,6 +267,13 @@ struct netfs_cache_ops {
 			     loff_t *_start, size_t *_len, loff_t i_size,
 			     bool no_space_allocated_yet);
 
+	/* Prepare an on-demand read operation, shortening it to a cached/uncached
+	 * boundary as appropriate.
+	 */
+	enum netfs_io_source (*prepare_ondemand_read)(struct netfs_cache_resources *cres,
+						      loff_t start, size_t *_len,
+						      loff_t i_size);
+
 	/* Query the occupancy of the cache in a region, returning where the
 	 * next chunk of data starts and how long it is.
 	 */
diff --git a/include/trace/events/cachefiles.h b/include/trace/events/cachefiles.h
index d8d4d73fe7b6..655d5900b8ef 100644
--- a/include/trace/events/cachefiles.h
+++ b/include/trace/events/cachefiles.h
@@ -448,14 +448,14 @@ TRACE_EVENT(cachefiles_prep_read,
 			     ),
 
 	    TP_fast_assign(
-		    __entry->rreq	= sreq->rreq->debug_id;
+		    __entry->rreq	= sreq->rreq ? sreq->rreq->debug_id : 0;
 		    __entry->index	= sreq->debug_index;
 		    __entry->flags	= sreq->flags;
 		    __entry->source	= source;
 		    __entry->why	= why;
 		    __entry->len	= sreq->len;
 		    __entry->start	= sreq->start;
-		    __entry->netfs_inode = sreq->rreq->inode->i_ino;
+		    __entry->netfs_inode = sreq->rreq ? sreq->rreq->inode->i_ino : 0;
 		    __entry->cache_inode = cache_inode;
 			   ),
 
-- 
2.19.1.6.gb485710b