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[V9fs-developer] [RFC PATCH 69/76] fscache: Add support for writing to the cache
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From: David H. <dho...@re...> - 2020-11-20 15:18:30
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Add a pair of helpers for use by a netfs to write data to the cache.
Signed-off-by: David Howells <dho...@re...>
---
fs/cachefiles/content-map.c | 38 +++++++++++++
fs/cachefiles/interface.c | 1
fs/cachefiles/internal.h | 2 +
fs/fscache/io.c | 128 +++++++++++++++++++++++++++++++++++++++++++
include/linux/fscache.h | 34 +++++++++++
5 files changed, 203 insertions(+)
diff --git a/fs/cachefiles/content-map.c b/fs/cachefiles/content-map.c
index da0a81e3f751..d1e8a509a8cc 100644
--- a/fs/cachefiles/content-map.c
+++ b/fs/cachefiles/content-map.c
@@ -204,6 +204,44 @@ enum netfs_read_source cachefiles_prepare_read(struct netfs_read_subrequest *sub
return NETFS_READ_FROM_CACHE;
}
+/*
+ * Prepare for a write to occur.
+ */
+int cachefiles_prepare_write(struct fscache_op_resources *opr,
+ loff_t *_start, size_t *_len, loff_t i_size)
+{
+ struct cachefiles_object *object =
+ container_of(opr->object, struct cachefiles_object, fscache);
+ loff_t start = *_start, map_limit;
+ size_t len = *_len, down;
+ long granule = start / CACHEFILES_GRAN_SIZE;
+
+ if (start >= CACHEFILES_SIZE_LIMIT)
+ return -ENOBUFS;
+
+ if (granule / 8 >= object->content_map_size) {
+ cachefiles_expand_content_map(object, i_size);
+ if (granule / 8 >= object->content_map_size)
+ return -ENOBUFS;
+ }
+
+ map_limit = object->content_map_size * 8 * CACHEFILES_GRAN_SIZE;
+ if (start >= map_limit)
+ return -ENOBUFS;
+ if (len > map_limit - start)
+ len = map_limit - start;
+
+ /* Assume that the preparation to write involved preloading any
+ * bits of the cache that weren't to be written and filling any
+ * gaps that didn't end up being written.
+ */
+
+ down = start - round_down(start, CACHEFILES_DIO_BLOCK_SIZE);
+ *_start = start - down;
+ *_len = round_up(down + len, CACHEFILES_DIO_BLOCK_SIZE);
+ return 0;
+}
+
/*
* Allocate a new content map.
*/
diff --git a/fs/cachefiles/interface.c b/fs/cachefiles/interface.c
index 3609ff2fb491..a9725ca72ad5 100644
--- a/fs/cachefiles/interface.c
+++ b/fs/cachefiles/interface.c
@@ -609,6 +609,7 @@ static const struct fscache_op_ops cachefiles_io_ops = {
.write = cachefiles_write,
.expand_readahead = cachefiles_expand_readahead,
.prepare_read = cachefiles_prepare_read,
+ .prepare_write = cachefiles_prepare_write,
};
static void cachefiles_begin_operation(struct fscache_op_resources *opr)
diff --git a/fs/cachefiles/internal.h b/fs/cachefiles/internal.h
index e2d06c0860a2..38149868c331 100644
--- a/fs/cachefiles/internal.h
+++ b/fs/cachefiles/internal.h
@@ -137,6 +137,8 @@ extern void cachefiles_mark_content_map(struct cachefiles_object *object,
loff_t start, loff_t len, unsigned int inval_counter);
extern void cachefiles_expand_content_map(struct cachefiles_object *object, loff_t size);
extern void cachefiles_shorten_content_map(struct cachefiles_object *object, loff_t new_size);
+extern int cachefiles_prepare_write(struct fscache_op_resources *opr,
+ loff_t *_start, size_t *_len, loff_t i_size);
extern bool cachefiles_load_content_map(struct cachefiles_object *object);
extern void cachefiles_save_content_map(struct cachefiles_object *object);
extern int cachefiles_display_object(struct seq_file *m, struct fscache_object *object);
diff --git a/fs/fscache/io.c b/fs/fscache/io.c
index 5401c9ed347b..295a89af4269 100644
--- a/fs/fscache/io.c
+++ b/fs/fscache/io.c
@@ -10,6 +10,7 @@
#include <linux/fscache-cache.h>
#include <linux/slab.h>
#include <linux/netfs.h>
+#include <linux/uio.h>
#include "internal.h"
/*
@@ -260,3 +261,130 @@ void __fscache_resize_cookie(struct fscache_cookie *cookie, loff_t new_size)
}
}
EXPORT_SYMBOL(__fscache_resize_cookie);
+
+struct fscache_write_request {
+ struct fscache_op_resources cache_resources;
+ struct address_space *mapping;
+ loff_t start;
+ size_t len;
+ fscache_io_terminated_t term_func;
+ void *term_func_priv;
+};
+
+/**
+ * fscache_clear_page_bits - Clear the PG_fscache bits from a set of pages
+ * @mapping: The netfs inode to use as the source
+ * @start: The start position in @mapping
+ * @len: The amount of data to unlock
+ *
+ * Clear the PG_fscache flag from a sequence of pages and wake up anyone who's
+ * waiting.
+ */
+void __fscache_clear_page_bits(struct address_space *mapping,
+ loff_t start, size_t len)
+{
+ pgoff_t first = start / PAGE_SIZE;
+ pgoff_t last = (start + len - 1) / PAGE_SIZE;
+ struct page *page;
+
+ if (len) {
+ XA_STATE(xas, &mapping->i_pages, first);
+
+ rcu_read_lock();
+ xas_for_each(&xas, page, last) {
+ unlock_page_fscache(page);
+ }
+ rcu_read_unlock();
+ }
+}
+EXPORT_SYMBOL(__fscache_clear_page_bits);
+
+/*
+ * Deal with the completion of writing the data to the cache.
+ */
+static void fscache_wreq_done(void *priv, ssize_t transferred_or_error)
+{
+ struct fscache_write_request *wreq = priv;
+
+ fscache_clear_page_bits(wreq->mapping, wreq->start, wreq->len);
+
+ if (wreq->term_func)
+ wreq->term_func(wreq->term_func_priv, transferred_or_error);
+ fscache_end_operation(&wreq->cache_resources);
+ kfree(wreq);
+}
+
+/**
+ * fscache_write_to_cache - Save a write to the cache and clear PG_fscache
+ * @cookie: The cookie representing the cache object
+ * @mapping: The netfs inode to use as the source
+ * @start: The start position in @mapping
+ * @len: The amount of data to write back
+ * @i_size: The new size of the inode
+ * @term_func: The function to call upon completion
+ * @term_func_priv: The private data for @term_func
+ *
+ * Helper function for a netfs to write dirty data from an inode into the cache
+ * object that's backing it.
+ *
+ * @start and @len describe the range of the data. This does not need to be
+ * page-aligned, but to satisfy DIO requirements, the cache may expand it up to
+ * the page boundaries on either end. All the pages covering the range must be
+ * marked with PG_fscache.
+ *
+ * If given, @term_func will be called upon completion and supplied with
+ * @term_func_priv. Note that the PG_fscache flags will have been cleared by
+ * this point, so the netfs must retain its own pin on the mapping.
+ */
+void __fscache_write_to_cache(struct fscache_cookie *cookie,
+ struct address_space *mapping,
+ loff_t start, size_t len, loff_t i_size,
+ fscache_io_terminated_t term_func,
+ void *term_func_priv)
+{
+ struct fscache_write_request *wreq;
+ struct fscache_op_resources *opr;
+ struct iov_iter iter;
+ int ret = -ENOBUFS;
+
+ if (!fscache_cookie_valid(cookie) || len == 0)
+ goto abandon;
+
+ _enter("%llx,%zx", start, len);
+
+ wreq = kzalloc(sizeof(struct fscache_write_request), GFP_NOFS);
+ if (!wreq)
+ goto abandon;
+ wreq->mapping = mapping;
+ wreq->start = start;
+ wreq->len = len;
+ wreq->term_func = term_func;
+ wreq->term_func_priv = term_func_priv;
+
+ opr = &wreq->cache_resources;
+ if (fscache_begin_operation(cookie, opr, FSCACHE_WANT_WRITE) < 0)
+ goto abandon_free;
+
+ ret = opr->ops->prepare_write(opr, &start, &len, i_size);
+ if (ret < 0)
+ goto abandon_end;
+
+ /* TODO: Consider clearing page bits now for space the write isn't
+ * covering. This is more complicated than it appears when THPs are
+ * taken into account.
+ */
+
+ iov_iter_xarray(&iter, WRITE, &mapping->i_pages, start, len);
+ fscache_write(opr, start, &iter, fscache_wreq_done, wreq);
+ return;
+
+abandon_end:
+ return fscache_wreq_done(wreq, ret);
+abandon_free:
+ kfree(wreq);
+abandon:
+ fscache_clear_page_bits(mapping, start, len);
+ if (term_func)
+ term_func(term_func_priv, ret);
+}
+EXPORT_SYMBOL(__fscache_write_to_cache);
diff --git a/include/linux/fscache.h b/include/linux/fscache.h
index 1c1ea3558421..0613ccea88c1 100644
--- a/include/linux/fscache.h
+++ b/include/linux/fscache.h
@@ -192,6 +192,12 @@ struct fscache_op_ops {
*/
enum netfs_read_source (*prepare_read)(struct netfs_read_subrequest *subreq,
loff_t i_size);
+
+ /* Prepare a write operation, working out what part of the write we can
+ * actually do.
+ */
+ int (*prepare_write)(struct fscache_op_resources *opr,
+ loff_t *_start, size_t *_len, loff_t i_size);
};
/*
@@ -226,6 +232,10 @@ extern void __fscache_invalidate(struct fscache_cookie *, const void *, loff_t,
extern void fscache_put_super(struct super_block *,
struct fscache_cookie *(*get_cookie)(struct inode *));
+extern void __fscache_write_to_cache(struct fscache_cookie *, struct address_space *,
+ loff_t, size_t, loff_t, fscache_io_terminated_t, void *);
+extern void __fscache_clear_page_bits(struct address_space *, loff_t, size_t);
+
/**
* fscache_register_netfs - Register a filesystem as desiring caching services
* @netfs: The description of the filesystem
@@ -627,6 +637,30 @@ int fscache_write(struct fscache_op_resources *opr,
return ops->write(opr, start_pos, iter, term_func, term_func_priv);
}
+static inline void fscache_clear_page_bits(struct address_space *mapping,
+ loff_t start, size_t len)
+{
+ if (fscache_available())
+ __fscache_clear_page_bits(mapping, start, len);
+}
+
+static inline void fscache_write_to_cache(struct fscache_cookie *cookie,
+ struct address_space *mapping,
+ loff_t start, size_t len, loff_t i_size,
+ fscache_io_terminated_t term_func,
+ void *term_func_priv)
+{
+ if (fscache_available()) {
+ __fscache_write_to_cache(cookie, mapping, start, len, i_size,
+ term_func, term_func_priv);
+ } else {
+ fscache_clear_page_bits(mapping, start, len);
+ if (term_func)
+ term_func(term_func_priv, -ENOBUFS);
+ }
+
+}
+
#if __fscache_available
extern int fscache_set_page_dirty(struct page *page, struct fscache_cookie *cookie);
#else
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