Provide a pair of functions to perform raw I/O on the cache. The first
function allows an arbitrary asynchronous direct-IO read to be made against
a cache object, though the read should be aligned and sized appropriately
for the backing device:
int fscache_read(struct netfs_cache_resources *cres,
loff_t start_pos,
struct iov_iter *iter,
enum netfs_read_from_hole read_hole,
netfs_io_terminated_t term_func,
void *term_func_priv);
The cache resources must have been previously initialised by
fscache_begin_read_operation(). A read operation is sent to the backing
filesystem, starting at start_pos within the file. The size of the read is
specified by the iterator, as is the location of the output buffer.
If there is a hole in the data it can be ignored and left to the backing
filesystem to deal with (NETFS_READ_HOLE_IGNORE), a hole at the beginning
can be skipped over and the buffer padded with zeros
(NETFS_READ_HOLE_CLEAR) or -ENODATA can be given (NETFS_READ_HOLE_FAIL).
If term_func is not NULL, the operation may be performed asynchronously.
Upon completion, successful or otherwise, (*term_func)() will be called and
passed term_func_priv, along with an error or the amount of data
transferred. If the op is run asynchronously, fscache_read() will return
-EIOCBQUEUED.
The second function allows an arbitrary asynchronous direct-IO write to be
made against a cache object, though the write should be aligned and sized
appropriately for the backing device:
int fscache_write(struct netfs_cache_resources *cres,
loff_t start_pos,
struct iov_iter *iter,
netfs_io_terminated_t term_func,
void *term_func_priv);
This works in very similar way to fscache_read(), except that there's no
need to deal with holes (they're just overwritten).
The caller is responsible for preventing concurrent overlapping writes.
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: linux-cachefs@xxxxxxxxxx
Link: https://lore.kernel.org/r/163819613224.215744.7877577215582621254.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v1
---
include/linux/fscache.h | 74 ++++++++++++++++++++++++++++++++++++++++
include/trace/events/fscache.h | 2 +
2 files changed, 76 insertions(+)
diff --git a/include/linux/fscache.h b/include/linux/fscache.h
index ceb1966acc52..55ea296fe4db 100644
--- a/include/linux/fscache.h
+++ b/include/linux/fscache.h
@@ -425,4 +425,78 @@ int fscache_begin_read_operation(struct netfs_cache_resources *cres,
return -ENOBUFS;
}
+/**
+ * fscache_read - Start a read from the cache.
+ * @cres: The cache resources to use
+ * @start_pos: The beginning file offset in the cache file
+ * @iter: The buffer to fill - and also the length
+ * @read_hole: How to handle a hole in the data.
+ * @term_func: The function to call upon completion
+ * @term_func_priv: The private data for @term_func
+ *
+ * Start a read from the cache. @cres indicates the cache object to read from
+ * and must be obtained by a call to fscache_begin_operation() beforehand.
+ *
+ * The data is read into the iterator, @iter, and that also indicates the size
+ * of the operation. @start_pos is the start position in the file, though if
+ * @seek_data is set appropriately, the cache can use SEEK_DATA to find the
+ * next piece of data, writing zeros for the hole into the iterator.
+ *
+ * Upon termination of the operation, @term_func will be called and supplied
+ * with @term_func_priv plus the amount of data written, if successful, or the
+ * error code otherwise.
+ *
+ * @read_hole indicates how a partially populated region in the cache should be
+ * handled. It can be one of a number of settings:
+ *
+ * NETFS_READ_HOLE_IGNORE - Just try to read (may return a short read).
+ *
+ * NETFS_READ_HOLE_CLEAR - Seek for data, clearing the part of the buffer
+ * skipped over, then do as for IGNORE.
+ *
+ * NETFS_READ_HOLE_FAIL - Give ENODATA if we encounter a hole.
+ */
+static inline
+int fscache_read(struct netfs_cache_resources *cres,
+ loff_t start_pos,
+ struct iov_iter *iter,
+ enum netfs_read_from_hole read_hole,
+ netfs_io_terminated_t term_func,
+ void *term_func_priv)
+{
+ const struct netfs_cache_ops *ops = fscache_operation_valid(cres);
+ return ops->read(cres, start_pos, iter, read_hole,
+ term_func, term_func_priv);
+}
+
+/**
+ * fscache_write - Start a write to the cache.
+ * @cres: The cache resources to use
+ * @start_pos: The beginning file offset in the cache file
+ * @iter: The data to write - and also the length
+ * @term_func: The function to call upon completion
+ * @term_func_priv: The private data for @term_func
+ *
+ * Start a write to the cache. @cres indicates the cache object to write to and
+ * must be obtained by a call to fscache_begin_operation() beforehand.
+ *
+ * The data to be written is obtained from the iterator, @iter, and that also
+ * indicates the size of the operation. @start_pos is the start position in
+ * the file.
+ *
+ * Upon termination of the operation, @term_func will be called and supplied
+ * with @term_func_priv plus the amount of data written, if successful, or the
+ * error code otherwise.
+ */
+static inline
+int fscache_write(struct netfs_cache_resources *cres,
+ loff_t start_pos,
+ struct iov_iter *iter,
+ netfs_io_terminated_t term_func,
+ void *term_func_priv)
+{
+ const struct netfs_cache_ops *ops = fscache_operation_valid(cres);
+ return ops->write(cres, start_pos, iter, term_func, term_func_priv);
+}
+
#endif /* _LINUX_FSCACHE_H */
diff --git a/include/trace/events/fscache.h b/include/trace/events/fscache.h
index 9f78c903b00a..2459d75659cf 100644
--- a/include/trace/events/fscache.h
+++ b/include/trace/events/fscache.h
@@ -79,6 +79,7 @@ enum fscache_access_trace {
fscache_access_io_not_live,
fscache_access_io_read,
fscache_access_io_wait,
+ fscache_access_io_write,
fscache_access_lookup_cookie,
fscache_access_lookup_cookie_end,
fscache_access_lookup_cookie_end_failed,
@@ -149,6 +150,7 @@ enum fscache_access_trace {
EM(fscache_access_io_not_live, "END io_notl") \
EM(fscache_access_io_read, "BEGIN io_read") \
EM(fscache_access_io_wait, "WAIT io ") \
+ EM(fscache_access_io_write, "BEGIN io_writ") \
EM(fscache_access_lookup_cookie, "BEGIN lookup ") \
EM(fscache_access_lookup_cookie_end, "END lookup ") \
EM(fscache_access_lookup_cookie_end_failed,"END lookupf") \
