Add a netfs_cache_ops method by which a network filesystem can ask the
cache about what data it has available and where so that it can make a
multipage read more efficient.
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: linux-cachefs@xxxxxxxxxx
---
Documentation/filesystems/netfs_library.rst | 16 +++++++
fs/cachefiles/io.c | 59 +++++++++++++++++++++++++++
include/linux/netfs.h | 7 +++
3 files changed, 82 insertions(+)
diff --git a/Documentation/filesystems/netfs_library.rst b/Documentation/filesystems/netfs_library.rst
index 136f8da3d0e2..4f373a8ec47b 100644
--- a/Documentation/filesystems/netfs_library.rst
+++ b/Documentation/filesystems/netfs_library.rst
@@ -462,6 +462,10 @@ operation table looks like the following::
struct iov_iter *iter,
netfs_io_terminated_t term_func,
void *term_func_priv);
+
+ int (*query_occupancy)(struct netfs_cache_resources *cres,
+ loff_t start, size_t len, size_t granularity,
+ loff_t *_data_start, size_t *_data_len);
};
With a termination handler function pointer::
@@ -536,6 +540,18 @@ The methods defined in the table are:
indicating whether the termination is definitely happening in the caller's
context.
+ * ``query_occupancy()``
+
+ [Required] Called to find out where the next piece of data is within a
+ particular region of the cache. The start and length of the region to be
+ queried are passed in, along with the granularity to which the answer needs
+ to be aligned. The function passes back the start and length of the data,
+ if any, available within that region. Note that there may be a hole at the
+ front.
+
+ It returns 0 if some data was found, -ENODATA if there was no usable data
+ within the region or -ENOBUFS if there is no caching on this file.
+
Note that these methods are passed a pointer to the cache resource structure,
not the read request structure as they could be used in other situations where
there isn't a read request structure as well, such as writing dirty data to the
diff --git a/fs/cachefiles/io.c b/fs/cachefiles/io.c
index 04eb52736990..753986ea1583 100644
--- a/fs/cachefiles/io.c
+++ b/fs/cachefiles/io.c
@@ -191,6 +191,64 @@ static int cachefiles_read(struct netfs_cache_resources *cres,
return ret;
}
+/*
+ * Query the occupancy of the cache in a region, returning where the next chunk
+ * of data starts and how long it is.
+ */
+static int cachefiles_query_occupancy(struct netfs_cache_resources *cres,
+ loff_t start, size_t len, size_t granularity,
+ loff_t *_data_start, size_t *_data_len)
+{
+ struct cachefiles_object *object;
+ struct file *file;
+ loff_t off, off2;
+
+ *_data_start = -1;
+ *_data_len = 0;
+
+ if (!fscache_wait_for_operation(cres, FSCACHE_WANT_READ))
+ return -ENOBUFS;
+
+ object = cachefiles_cres_object(cres);
+ file = cachefiles_cres_file(cres);
+ granularity = max_t(size_t, object->volume->cache->bsize, granularity);
+
+ _enter("%pD,%li,%llx,%zx/%llx",
+ file, file_inode(file)->i_ino, start, len,
+ i_size_read(file_inode(file)));
+
+ off = cachefiles_inject_read_error();
+ if (off == 0)
+ off = vfs_llseek(file, start, SEEK_DATA);
+ if (off == -ENXIO)
+ return -ENODATA; /* Beyond EOF */
+ if (off < 0 && off >= (loff_t)-MAX_ERRNO)
+ return -ENOBUFS; /* Error. */
+ if (round_up(off, granularity) >= start + len)
+ return -ENODATA; /* No data in range */
+
+ off2 = cachefiles_inject_read_error();
+ if (off2 == 0)
+ off2 = vfs_llseek(file, off, SEEK_HOLE);
+ if (off2 == -ENXIO)
+ return -ENODATA; /* Beyond EOF */
+ if (off2 < 0 && off2 >= (loff_t)-MAX_ERRNO)
+ return -ENOBUFS; /* Error. */
+
+ /* Round away partial blocks */
+ off = round_up(off, granularity);
+ off2 = round_down(off2, granularity);
+ if (off2 <= off)
+ return -ENODATA;
+
+ *_data_start = off;
+ if (off2 > start + len)
+ *_data_len = len;
+ else
+ *_data_len = off2 - off;
+ return 0;
+}
+
/*
* Handle completion of a write to the cache.
*/
@@ -545,6 +603,7 @@ static const struct netfs_cache_ops cachefiles_netfs_cache_ops = {
.write = cachefiles_write,
.prepare_read = cachefiles_prepare_read,
.prepare_write = cachefiles_prepare_write,
+ .query_occupancy = cachefiles_query_occupancy,
};
/*
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index b46c39d98bbd..614f22213e21 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -244,6 +244,13 @@ 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);
+
+ /* Query the occupancy of the cache in a region, returning where the
+ * next chunk of data starts and how long it is.
+ */
+ int (*query_occupancy)(struct netfs_cache_resources *cres,
+ loff_t start, size_t len, size_t granularity,
+ loff_t *_data_start, size_t *_data_len);
};
struct readahead_control;
--
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