netfs: Add a netfs inode context

Add a netfs_i_context struct that should be included in the network
filesystem's own inode struct wrapper, directly after the VFS's inode
struct, e.g.:

	struct my_inode {
		struct {
			/* These must be contiguous */
			struct inode		vfs_inode;
			struct netfs_i_context	netfs_ctx;
		};
	};

The netfs_i_context struct so far contains a single field for the network
filesystem to use - the cache cookie:

	struct netfs_i_context {
		...
		struct fscache_cookie	*cache;
	};

Three functions are provided to help with this:

 (1) void netfs_i_context_init(struct inode *inode,
			       const struct netfs_request_ops *ops);

     Initialise the netfs context and set the operations.

 (2) struct netfs_i_context *netfs_i_context(struct inode *inode);

     Find the netfs context from the VFS inode.

 (3) struct inode *netfs_inode(struct netfs_i_context *ctx);

     Find the VFS inode from the netfs context.

Changes
=======
ver #4)
 - Fix netfs_is_cache_enabled() to check cookie->cache_priv to see if a
   cache is present[3].
 - Fix netfs_skip_folio_read() to zero out all of the page, not just some
   of it[3].

ver #3)
 - Split out the bit to move ceph cap-getting on readahead into
   ceph_init_request()[1].
 - Stick in a comment to the netfs inode structs indicating the contiguity
   requirements[2].

ver #2)
 - Adjust documentation to match.
 - Use "#if IS_ENABLED()" in netfs_i_cookie(), not "#ifdef".
 - Move the cap check from ceph_readahead() to ceph_init_request() to be
   called from netfslib.
 - Remove ceph_readahead() and use  netfs_readahead() directly instead.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com

Link: https://lore.kernel.org/r/8af0d47f17d89c06bbf602496dd845f2b0bf25b3.camel@kernel.org/ [1]
Link: https://lore.kernel.org/r/beaf4f6a6c2575ed489adb14b257253c868f9a5c.camel@kernel.org/ [2]
Link: https://lore.kernel.org/r/3536452.1647421585@warthog.procyon.org.uk/ [3]
Link: https://lore.kernel.org/r/164622984545.3564931.15691742939278418580.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/164678213320.1200972.16807551936267647470.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/164692909854.2099075.9535537286264248057.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/306388.1647595110@warthog.procyon.org.uk/ # v4

4 files changed, 67 insertions, 64 deletions

diff --git a/fs/netfs/internal.h b/fs/netfs/internal.h
index 89837e904fa7..54c761bcc8e6 100644
--- a/fs/netfs/internal.h
+++ b/fs/netfs/internal.h
@@ -6,6 +6,7 @@
  */
 
 #include <linux/netfs.h>
+#include <linux/fscache.h>
 #include <trace/events/netfs.h>
 
 #ifdef pr_fmt
@@ -19,8 +20,6 @@
  */
 struct netfs_io_request *netfs_alloc_request(struct address_space *mapping,
 					     struct file *file,
-					     const struct netfs_request_ops *ops,
-					     void *netfs_priv,
 					     loff_t start, size_t len,
 					     enum netfs_io_origin origin);
 void netfs_get_request(struct netfs_io_request *rreq, enum netfs_rreq_ref_trace what);
@@ -81,6 +80,21 @@ static inline void netfs_stat_d(atomic_t *stat)
 #define netfs_stat_d(x) do {} while(0)
 #endif
 
+/*
+ * Miscellaneous functions.
+ */
+static inline bool netfs_is_cache_enabled(struct netfs_i_context *ctx)
+{
+#if IS_ENABLED(CONFIG_FSCACHE)
+	struct fscache_cookie *cookie = ctx->cache;
+
+	return fscache_cookie_valid(cookie) && cookie->cache_priv &&
+		fscache_cookie_enabled(cookie);
+#else
+	return false;
+#endif
+}
+
 /*****************************************************************************/
 /*
  * debug tracing
diff --git a/fs/netfs/objects.c b/fs/netfs/objects.c
index ae18827e156b..657b19e60118 100644
--- a/fs/netfs/objects.c
+++ b/fs/netfs/objects.c
@@ -13,12 +13,12 @@
  */
 struct netfs_io_request *netfs_alloc_request(struct address_space *mapping,
 					     struct file *file,
-					     const struct netfs_request_ops *ops,
-					     void *netfs_priv,
 					     loff_t start, size_t len,
 					     enum netfs_io_origin origin)
 {
 	static atomic_t debug_ids;
+	struct inode *inode = file ? file_inode(file) : mapping->host;
+	struct netfs_i_context *ctx = netfs_i_context(inode);
 	struct netfs_io_request *rreq;
 	int ret;
 
@@ -29,11 +29,10 @@ struct netfs_io_request *netfs_alloc_request(struct address_space *mapping,
 	rreq->start	= start;
 	rreq->len	= len;
 	rreq->origin	= origin;
-	rreq->netfs_ops	= ops;
-	rreq->netfs_priv = netfs_priv;
+	rreq->netfs_ops	= ctx->ops;
 	rreq->mapping	= mapping;
-	rreq->inode	= file_inode(file);
-	rreq->i_size	= i_size_read(rreq->inode);
+	rreq->inode	= inode;
+	rreq->i_size	= i_size_read(inode);
 	rreq->debug_id	= atomic_inc_return(&debug_ids);
 	INIT_LIST_HEAD(&rreq->subrequests);
 	INIT_WORK(&rreq->work, netfs_rreq_work);
@@ -76,6 +75,7 @@ static void netfs_free_request(struct work_struct *work)
 {
 	struct netfs_io_request *rreq =
 		container_of(work, struct netfs_io_request, work);
+
 	netfs_clear_subrequests(rreq, false);
 	if (rreq->netfs_priv)
 		rreq->netfs_ops->cleanup(rreq->mapping, rreq->netfs_priv);
diff --git a/fs/netfs/read_helper.c b/fs/netfs/read_helper.c
index b5176f4320f4..c048cd328ce5 100644
--- a/fs/netfs/read_helper.c
+++ b/fs/netfs/read_helper.c
@@ -14,7 +14,6 @@
 #include <linux/uio.h>
 #include <linux/sched/mm.h>
 #include <linux/task_io_accounting_ops.h>
-#include <linux/netfs.h>
 #include "internal.h"
 #define CREATE_TRACE_POINTS
 #include <trace/events/netfs.h>
@@ -735,8 +734,6 @@ static void netfs_rreq_expand(struct netfs_io_request *rreq,
 /**
  * netfs_readahead - Helper to manage a read request
  * @ractl: The description of the readahead request
- * @ops: The network filesystem's operations for the helper to use
- * @netfs_priv: Private netfs data to be retained in the request
  *
  * Fulfil a readahead request by drawing data from the cache if possible, or
  * the netfs if not.  Space beyond the EOF is zero-filled.  Multiple I/O
@@ -744,35 +741,32 @@ static void netfs_rreq_expand(struct netfs_io_request *rreq,
  * readahead window can be expanded in either direction to a more convenient
  * alighment for RPC efficiency or to make storage in the cache feasible.
  *
- * The calling netfs must provide a table of operations, only one of which,
- * issue_op, is mandatory.  It may also be passed a private token, which will
- * be retained in rreq->netfs_priv and will be cleaned up by ops->cleanup().
+ * The calling netfs must initialise a netfs context contiguous to the vfs
+ * inode before calling this.
  *
  * This is usable whether or not caching is enabled.
  */
-void netfs_readahead(struct readahead_control *ractl,
-		     const struct netfs_request_ops *ops,
-		     void *netfs_priv)
+void netfs_readahead(struct readahead_control *ractl)
 {
 	struct netfs_io_request *rreq;
+	struct netfs_i_context *ctx = netfs_i_context(ractl->mapping->host);
 	unsigned int debug_index = 0;
 	int ret;
 
 	_enter("%lx,%x", readahead_index(ractl), readahead_count(ractl));
 
 	if (readahead_count(ractl) == 0)
-		goto cleanup;
+		return;
 
 	rreq = netfs_alloc_request(ractl->mapping, ractl->file,
-				   ops, netfs_priv,
 				   readahead_pos(ractl),
 				   readahead_length(ractl),
 				   NETFS_READAHEAD);
 	if (IS_ERR(rreq))
-		goto cleanup;
+		return;
 
-	if (ops->begin_cache_operation) {
-		ret = ops->begin_cache_operation(rreq);
+	if (ctx->ops->begin_cache_operation) {
+		ret = ctx->ops->begin_cache_operation(rreq);
 		if (ret == -ENOMEM || ret == -EINTR || ret == -ERESTARTSYS)
 			goto cleanup_free;
 	}
@@ -804,42 +798,35 @@ void netfs_readahead(struct readahead_control *ractl,
 cleanup_free:
 	netfs_put_request(rreq, false, netfs_rreq_trace_put_failed);
 	return;
-cleanup:
-	if (netfs_priv)
-		ops->cleanup(ractl->mapping, netfs_priv);
-	return;
 }
 EXPORT_SYMBOL(netfs_readahead);
 
 /**
  * netfs_readpage - Helper to manage a readpage request
  * @file: The file to read from
- * @folio: The folio to read
- * @ops: The network filesystem's operations for the helper to use
- * @netfs_priv: Private netfs data to be retained in the request
+ * @subpage: A subpage of the folio to read
  *
  * Fulfil a readpage request by drawing data from the cache if possible, or the
  * netfs if not.  Space beyond the EOF is zero-filled.  Multiple I/O requests
  * from different sources will get munged together.
  *
- * The calling netfs must provide a table of operations, only one of which,
- * issue_op, is mandatory.  It may also be passed a private token, which will
- * be retained in rreq->netfs_priv and will be cleaned up by ops->cleanup().
+ * The calling netfs must initialise a netfs context contiguous to the vfs
+ * inode before calling this.
  *
  * This is usable whether or not caching is enabled.
  */
-int netfs_readpage(struct file *file,
-		   struct folio *folio,
-		   const struct netfs_request_ops *ops,
-		   void *netfs_priv)
+int netfs_readpage(struct file *file, struct page *subpage)
 {
+	struct folio *folio = page_folio(subpage);
+	struct address_space *mapping = folio->mapping;
 	struct netfs_io_request *rreq;
+	struct netfs_i_context *ctx = netfs_i_context(mapping->host);
 	unsigned int debug_index = 0;
 	int ret;
 
 	_enter("%lx", folio_index(folio));
 
-	rreq = netfs_alloc_request(folio->mapping, file, ops, netfs_priv,
+	rreq = netfs_alloc_request(mapping, file,
 				   folio_file_pos(folio), folio_size(folio),
 				   NETFS_READPAGE);
 	if (IS_ERR(rreq)) {
@@ -847,8 +834,8 @@ int netfs_readpage(struct file *file,
 		goto alloc_error;
 	}
 
-	if (ops->begin_cache_operation) {
-		ret = ops->begin_cache_operation(rreq);
+	if (ctx->ops->begin_cache_operation) {
+		ret = ctx->ops->begin_cache_operation(rreq);
 		if (ret == -ENOMEM || ret == -EINTR || ret == -ERESTARTSYS) {
 			folio_unlock(folio);
 			goto out;
@@ -886,8 +873,6 @@ out:
 	netfs_put_request(rreq, false, netfs_rreq_trace_put_hold);
 	return ret;
 alloc_error:
-	if (netfs_priv)
-		ops->cleanup(folio_file_mapping(folio), netfs_priv);
 	folio_unlock(folio);
 	return ret;
 }
@@ -898,6 +883,7 @@ EXPORT_SYMBOL(netfs_readpage);
  * @folio: The folio being prepared
  * @pos: starting position for the write
  * @len: length of write
+ * @always_fill: T if the folio should always be completely filled/cleared
  *
  * In some cases, write_begin doesn't need to read at all:
  * - full folio write
@@ -907,17 +893,27 @@ EXPORT_SYMBOL(netfs_readpage);
  * If any of these criteria are met, then zero out the unwritten parts
  * of the folio and return true. Otherwise, return false.
  */
-static bool netfs_skip_folio_read(struct folio *folio, loff_t pos, size_t len)
+static bool netfs_skip_folio_read(struct folio *folio, loff_t pos, size_t len,
+				 bool always_fill)
 {
 	struct inode *inode = folio_inode(folio);
 	loff_t i_size = i_size_read(inode);
 	size_t offset = offset_in_folio(folio, pos);
+	size_t plen = folio_size(folio);
+
+	if (unlikely(always_fill)) {
+		if (pos - offset + len <= i_size)
+			return false; /* Page entirely before EOF */
+		zero_user_segment(&folio->page, 0, plen);
+		folio_mark_uptodate(folio);
+		return true;
+	}
 
 	/* Full folio write */
-	if (offset == 0 && len >= folio_size(folio))
+	if (offset == 0 && len >= plen)
 		return true;
 
-	/* pos beyond last folio in the file */
+	/* Page entirely beyond the end of the file */
 	if (pos - offset >= i_size)
 		goto zero_out;
 
@@ -927,7 +923,7 @@ static bool netfs_skip_folio_read(struct folio *folio, loff_t pos, size_t len)
 
 	return false;
 zero_out:
-	zero_user_segments(&folio->page, 0, offset, offset + len, folio_size(folio));
+	zero_user_segments(&folio->page, 0, offset, offset + len, plen);
 	return true;
 }
 
@@ -940,8 +936,6 @@ zero_out:
  * @aop_flags: AOP_* flags
  * @_folio: Where to put the resultant folio
  * @_fsdata: Place for the netfs to store a cookie
- * @ops: The network filesystem's operations for the helper to use
- * @netfs_priv: Private netfs data to be retained in the request
  *
  * Pre-read data for a write-begin request by drawing data from the cache if
  * possible, or the netfs if not.  Space beyond the EOF is zero-filled.
@@ -960,17 +954,18 @@ zero_out:
  * should go ahead; unlock the folio and return -EAGAIN to cause the folio to
  * be regot; or return an error.
  *
+ * The calling netfs must initialise a netfs context contiguous to the vfs
+ * inode before calling this.
+ *
  * This is usable whether or not caching is enabled.
  */
 int netfs_write_begin(struct file *file, struct address_space *mapping,
 		      loff_t pos, unsigned int len, unsigned int aop_flags,
-		      struct folio **_folio, void **_fsdata,
-		      const struct netfs_request_ops *ops,
-		      void *netfs_priv)
+		      struct folio **_folio, void **_fsdata)
 {
 	struct netfs_io_request *rreq;
+	struct netfs_i_context *ctx = netfs_i_context(file_inode(file ));
 	struct folio *folio;
-	struct inode *inode = file_inode(file);
 	unsigned int debug_index = 0, fgp_flags;
 	pgoff_t index = pos >> PAGE_SHIFT;
 	int ret;
@@ -986,9 +981,9 @@ retry:
 	if (!folio)
 		return -ENOMEM;
 
-	if (ops->check_write_begin) {
+	if (ctx->ops->check_write_begin) {
 		/* Allow the netfs (eg. ceph) to flush conflicts. */
-		ret = ops->check_write_begin(file, pos, len, folio, _fsdata);
+		ret = ctx->ops->check_write_begin(file, pos, len, folio, _fsdata);
 		if (ret < 0) {
 			trace_netfs_failure(NULL, NULL, ret, netfs_fail_check_write_begin);
 			if (ret == -EAGAIN)
@@ -1004,13 +999,13 @@ retry:
 	 * within the cache granule containing the EOF, in which case we need
 	 * to preload the granule.
 	 */
-	if (!ops->is_cache_enabled(inode) &&
-	    netfs_skip_folio_read(folio, pos, len)) {
+	if (!netfs_is_cache_enabled(ctx) &&
+	    netfs_skip_folio_read(folio, pos, len, false)) {
 		netfs_stat(&netfs_n_rh_write_zskip);
 		goto have_folio_no_wait;
 	}
 
-	rreq = netfs_alloc_request(mapping, file, ops, netfs_priv,
+	rreq = netfs_alloc_request(mapping, file,
 				   folio_file_pos(folio), folio_size(folio),
 				   NETFS_READ_FOR_WRITE);
 	if (IS_ERR(rreq)) {
@@ -1019,10 +1014,9 @@ retry:
 	}
 	rreq->no_unlock_folio	= folio_index(folio);
 	__set_bit(NETFS_RREQ_NO_UNLOCK_FOLIO, &rreq->flags);
-	netfs_priv = NULL;
 
-	if (ops->begin_cache_operation) {
-		ret = ops->begin_cache_operation(rreq);
+	if (ctx->ops->begin_cache_operation) {
+		ret = ctx->ops->begin_cache_operation(rreq);
 		if (ret == -ENOMEM || ret == -EINTR || ret == -ERESTARTSYS)
 			goto error_put;
 	}
@@ -1076,8 +1070,6 @@ have_folio:
 	if (ret < 0)
 		goto error;
 have_folio_no_wait:
-	if (netfs_priv)
-		ops->cleanup(mapping, netfs_priv);
 	*_folio = folio;
 	_leave(" = 0");
 	return 0;
@@ -1087,8 +1079,6 @@ error_put:
 error:
 	folio_unlock(folio);
 	folio_put(folio);
-	if (netfs_priv)
-		ops->cleanup(mapping, netfs_priv);
 	_leave(" = %d", ret);
 	return ret;
 }
diff --git a/fs/netfs/stats.c b/fs/netfs/stats.c
index 9ae538c85378..5510a7a14a40 100644
--- a/fs/netfs/stats.c
+++ b/fs/netfs/stats.c
@@ -7,7 +7,6 @@
 
 #include <linux/export.h>
 #include <linux/seq_file.h>
-#include <linux/netfs.h>
 #include "internal.h"
 
 atomic_t netfs_n_rh_readahead;