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 <jeffl...@linux.alibaba.com>
---
fs/netfs/read_helper.c | 26 ++++++++++++++++++++++++++
include/linux/netfs.h | 4 ++++
2 files changed, 30 insertions(+)
diff --git a/fs/netfs/read_helper.c b/fs/netfs/read_helper.c
index ade1523fc180..3460cfd7a570 100644
--- a/fs/netfs/read_helper.c
+++ b/fs/netfs/read_helper.c
@@ -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
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index 5f45eb31defd..8a9dae361f07 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -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 *);
--
2.27.0
--
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