@@ -1125,6 +1125,32 @@ int netfs_readpage_demand(struct folio *folio,
}
EXPORT_SYMBOL(netfs_readpage_demand);
+void netfs_demand_read(struct netfs_read_subrequest *subreq)
+{
+ struct netfs_read_request *rreq = subreq->rreq;
+ struct netfs_cache_resources *cres = &rreq->cache_resources;
+ loff_t start_pos;
+ size_t len;
+ int ret;
+
+ start_pos = subreq->start + subreq->transferred;
+ len = subreq->len - subreq->transferred;
+
+ /*
+ * In success case (ret == 0), user daemon has downloaded data for us,
+ * thus transform to NETFS_READ_FROM_CACHE state and advertise that 0
+ * byte readed, so that the request will enter into INCOMPLETE state and
+ * re-read from backing file.
+ */
+ ret = cres->ops->demand_read(cres, start_pos, len);
+ if (!ret) {
+ subreq->source = NETFS_READ_FROM_CACHE;
+ __clear_bit(NETFS_SREQ_WRITE_TO_CACHE, &subreq->flags);
+ }
+
+ netfs_subreq_terminated(subreq, ret, false);
+}
+
/*
* Prepare a folio for writing without reading first
* @folio: The folio being prepared
@@ -253,6 +253,9 @@ struct netfs_cache_ops {
int (*prepare_write)(struct netfs_cache_resources *cres,
loff_t *_start, size_t *_len, loff_t i_size,
bool no_space_allocated_yet);
+
+ int (*demand_read)(struct netfs_cache_resources *cres,
+ loff_t start_pos, size_t len);
};
struct readahead_control;
@@ -271,6 +274,7 @@ extern int netfs_write_begin(struct file *, struct address_space *,
void **,
const struct netfs_read_request_ops *,
void *);
+extern void netfs_demand_read(struct netfs_read_subrequest *);
extern void netfs_subreq_terminated(struct netfs_read_subrequest *, ssize_t, bool);
extern void netfs_stats_show(struct seq_file *);
Add demand_read() callback to netfs_cache_ops to implement demand read. To implement demand-read semantics, the data blob file is a sparse file on the first beginning. When fs starts to access the data blob file, it will "cache miss" (hit the hole) and then .issue_op() callback will be called to prepare the data. .issue_op() callback could call netfs_demand_read() helper function introduced in this patch to prepare the data, which will in turn call .demand_read() callback of fscache backend. Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com> --- fs/netfs/read_helper.c | 26 ++++++++++++++++++++++++++ include/linux/netfs.h | 4 ++++ 2 files changed, 30 insertions(+)