ceph: Make ceph_init_request() check caps on readahead

Move the caps check from ceph_readahead() to ceph_init_request(),
conditional on the origin being NETFS_READAHEAD so that in a future patch,
ceph can point its ->readahead() vector directly at netfs_readahead().

Changes
=======
ver #4)
 - Move the check for NETFS_READAHEAD up in ceph_init_request()[2].

ver #3)
 - Split from the patch to add a netfs inode context[1].
 - Need to store the caps got in rreq->netfs_priv for later freeing.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: ceph-devel@vger.kernel.org
cc: linux-cachefs@redhat.com

Link: https://lore.kernel.org/r/8af0d47f17d89c06bbf602496dd845f2b0bf25b3.camel@kernel.org/ [1]
Link: https://lore.kernel.org/r/dd054c962818716e718bd9b446ee5322ca097675.camel@redhat.com/ [2]
Link: https://lore.kernel.org/r/164692907694.2099075.10081819855690054094.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/2533821.1647006574@warthog.procyon.org.uk/ # v4

fs/ceph/addr.c

@@ -354,6 +354,45 @@ out:
 	dout("%s: result %d\n", __func__, err);
 }
 
+static int ceph_init_request(struct netfs_io_request *rreq, struct file *file)
+{
+	struct inode *inode = rreq->inode;
+	int got = 0, want = CEPH_CAP_FILE_CACHE;
+	int ret = 0;
+
+	if (rreq->origin != NETFS_READAHEAD)
+		return 0;
+
+	if (file) {
+		struct ceph_rw_context *rw_ctx;
+		struct ceph_file_info *fi = file->private_data;
+
+		rw_ctx = ceph_find_rw_context(fi);
+		if (rw_ctx)
+			return 0;
+	}
+
+	/*
+	 * readahead callers do not necessarily hold Fcb caps
+	 * (e.g. fadvise, madvise).
+	 */
+	ret = ceph_try_get_caps(inode, CEPH_CAP_FILE_RD, want, true, &got);
+	if (ret < 0) {
+		dout("start_read %p, error getting cap\n", inode);
+		return ret;
+	}
+
+	if (!(got & want)) {
+		dout("start_read %p, no cache cap\n", inode);
+		return -EACCES;
+	}
+	if (ret == 0)
+		return -EACCES;
+
+	rreq->netfs_priv = (void *)(uintptr_t)got;
+	return 0;
+}
+
 static void ceph_readahead_cleanup(struct address_space *mapping, void *priv)
 {
 	struct inode *inode = mapping->host;
@@ -365,7 +404,7 @@ static void ceph_readahead_cleanup(struct address_space *mapping, void *priv)
 }
 
 static const struct netfs_request_ops ceph_netfs_read_ops = {
-	.is_cache_enabled	= ceph_is_cache_enabled,
+	.init_request		= ceph_init_request,
 	.begin_cache_operation	= ceph_begin_cache_operation,
 	.issue_read		= ceph_netfs_issue_read,
 	.expand_readahead	= ceph_netfs_expand_readahead,
@@ -393,33 +432,7 @@ static int ceph_readpage(struct file *file, struct page *subpage)
 
 static void ceph_readahead(struct readahead_control *ractl)
 {
-	struct inode *inode = file_inode(ractl->file);
+	netfs_readahead(ractl, &ceph_netfs_read_ops, NULL);
-	struct ceph_file_info *fi = ractl->file->private_data;
-	struct ceph_rw_context *rw_ctx;
-	int got = 0;
-	int ret = 0;
-
-	if (ceph_inode(inode)->i_inline_version != CEPH_INLINE_NONE)
-		return;
-
-	rw_ctx = ceph_find_rw_context(fi);
-	if (!rw_ctx) {
-		/*
-		 * readahead callers do not necessarily hold Fcb caps
-		 * (e.g. fadvise, madvise).
-		 */
-		int want = CEPH_CAP_FILE_CACHE;
-
-		ret = ceph_try_get_caps(inode, CEPH_CAP_FILE_RD, want, true, &got);
-		if (ret < 0)
-			dout("start_read %p, error getting cap\n", inode);
-		else if (!(got & want))
-			dout("start_read %p, no cache cap\n", inode);
-
-		if (ret <= 0)
-			return;
-	}
-	netfs_readahead(ractl, &ceph_netfs_read_ops, (void *)(uintptr_t)got);
 }
 
 #ifdef CONFIG_CEPH_FSCACHE