afs: Use netfslib for symlinks, allowing them to be cached

Use netfslib to read symlinks, thereby allowing them to be cached by
fscache and cachefiles.

Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/20241216204124.3752367-23-dhowells@redhat.com
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-afs@lists.infradead.org
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

fs/afs/file.c

@@ -20,7 +20,6 @@
 #include "internal.h"
 
 static int afs_file_mmap(struct file *file, struct vm_area_struct *vma);
-static int afs_symlink_read_folio(struct file *file, struct folio *folio);
 
 static ssize_t afs_file_read_iter(struct kiocb *iocb, struct iov_iter *iter);
 static ssize_t afs_file_splice_read(struct file *in, loff_t *ppos,
@@ -61,13 +60,6 @@ const struct address_space_operations afs_file_aops = {
 	.writepages	= afs_writepages,
 };
 
-const struct address_space_operations afs_symlink_aops = {
-	.read_folio	= afs_symlink_read_folio,
-	.release_folio	= netfs_release_folio,
-	.invalidate_folio = netfs_invalidate_folio,
-	.migrate_folio	= filemap_migrate_folio,
-};
-
 static const struct vm_operations_struct afs_vm_ops = {
 	.open		= afs_vm_open,
 	.close		= afs_vm_close,
@@ -346,30 +338,6 @@ static void afs_issue_read(struct netfs_io_subrequest *subreq)
 	queue_work(system_long_wq, &subreq->work);
 }
 
-static int afs_symlink_read_folio(struct file *file, struct folio *folio)
-{
-	struct afs_vnode *vnode = AFS_FS_I(folio->mapping->host);
-	struct afs_read *fsreq;
-	int ret;
-
-	fsreq = afs_alloc_read(GFP_NOFS);
-	if (!fsreq)
-		return -ENOMEM;
-
-	fsreq->pos	= folio_pos(folio);
-	fsreq->len	= folio_size(folio);
-	fsreq->vnode	= vnode;
-	fsreq->iter	= &fsreq->def_iter;
-	iov_iter_xarray(&fsreq->def_iter, ITER_DEST, &folio->mapping->i_pages,
-			fsreq->pos, fsreq->len);
-
-	ret = afs_fetch_data(fsreq->vnode, fsreq);
-	if (ret == 0)
-		folio_mark_uptodate(folio);
-	folio_unlock(folio);
-	return ret;
-}
-
 static int afs_init_request(struct netfs_io_request *rreq, struct file *file)
 {
 	struct afs_vnode *vnode = AFS_FS_I(rreq->inode);

fs/afs/inode.c

@@ -25,8 +25,60 @@
 #include "internal.h"
 #include "afs_fs.h"
 
+static void afs_put_link(void *arg)
+{
+	struct folio *folio = virt_to_folio(arg);
+
+	kunmap_local(arg);
+	folio_put(folio);
+}
+
+const char *afs_get_link(struct dentry *dentry, struct inode *inode,
+			 struct delayed_call *callback)
+{
+	struct afs_vnode *vnode = AFS_FS_I(inode);
+	struct folio *folio;
+	char *content;
+	ssize_t ret;
+
+	if (atomic64_read(&vnode->cb_expires_at) == AFS_NO_CB_PROMISE ||
+	    !test_bit(AFS_VNODE_DIR_READ, &vnode->flags)) {
+		if (!dentry)
+			return ERR_PTR(-ECHILD);
+		ret = afs_read_single(vnode, NULL);
+		if (ret < 0)
+			return ERR_PTR(ret);
+	}
+
+	folio = folioq_folio(vnode->directory, 0);
+	folio_get(folio);
+	content = kmap_local_folio(folio, 0);
+	set_delayed_call(callback, afs_put_link, content);
+	return content;
+}
+
+int afs_readlink(struct dentry *dentry, char __user *buffer, int buflen)
+{
+	DEFINE_DELAYED_CALL(done);
+	const char *content;
+	int len;
+
+	content = afs_get_link(dentry, d_inode(dentry), &done);
+	if (IS_ERR(content)) {
+		do_delayed_call(&done);
+		return PTR_ERR(content);
+	}
+
+	len = umin(strlen(content), buflen);
+	if (copy_to_user(buffer, content, len))
+		len = -EFAULT;
+	do_delayed_call(&done);
+	return len;
+}
+
 static const struct inode_operations afs_symlink_inode_operations = {
-	.get_link	= page_get_link,
+	.get_link	= afs_get_link,
+	.readlink	= afs_readlink,
 };
 
 static noinline void dump_vnode(struct afs_vnode *vnode, struct afs_vnode *parent_vnode)
@@ -124,13 +176,13 @@ static int afs_inode_init_from_status(struct afs_operation *op,
 			inode->i_mode	= S_IFDIR | 0555;
 			inode->i_op	= &afs_mntpt_inode_operations;
 			inode->i_fop	= &afs_mntpt_file_operations;
-			inode->i_mapping->a_ops	= &afs_symlink_aops;
 		} else {
 			inode->i_mode	= S_IFLNK | status->mode;
 			inode->i_op	= &afs_symlink_inode_operations;
-			inode->i_mapping->a_ops	= &afs_symlink_aops;
 		}
+		inode->i_mapping->a_ops	= &afs_dir_aops;
 		inode_nohighmem(inode);
+		mapping_set_release_always(inode->i_mapping);
 		break;
 	default:
 		dump_vnode(vnode, op->file[0].vnode != vnode ? op->file[0].vnode : NULL);
@@ -443,7 +495,8 @@ static void afs_get_inode_cache(struct afs_vnode *vnode)
 	struct afs_vnode_cache_aux aux;
 
 	if (vnode->status.type != AFS_FTYPE_FILE &&
-	    vnode->status.type != AFS_FTYPE_DIR) {
+	    vnode->status.type != AFS_FTYPE_DIR &&
+	    vnode->status.type != AFS_FTYPE_SYMLINK) {
 		vnode->netfs.cache = NULL;
 		return;
 	}
@@ -657,7 +710,8 @@ void afs_evict_inode(struct inode *inode)
 
 	ASSERTCMP(inode->i_ino, ==, vnode->fid.vnode);
 
-	if ((S_ISDIR(inode->i_mode)) &&
+	if ((S_ISDIR(inode->i_mode) ||
+	     S_ISLNK(inode->i_mode)) &&
 	    (inode->i_state & I_DIRTY) &&
 	    !sbi->dyn_root) {
 		struct writeback_control wbc = {

fs/afs/internal.h

@@ -1116,7 +1116,6 @@ extern void afs_dynroot_depopulate(struct super_block *);
  * file.c
  */
 extern const struct address_space_operations afs_file_aops;
-extern const struct address_space_operations afs_symlink_aops;
 extern const struct inode_operations afs_file_inode_operations;
 extern const struct file_operations afs_file_operations;
 extern const struct netfs_request_ops afs_req_ops;
@@ -1222,6 +1221,9 @@ extern void afs_fs_probe_cleanup(struct afs_net *);
  */
 extern const struct afs_operation_ops afs_fetch_status_operation;
 
+const char *afs_get_link(struct dentry *dentry, struct inode *inode,
+			 struct delayed_call *callback);
+int afs_readlink(struct dentry *dentry, char __user *buffer, int buflen);
 extern void afs_vnode_commit_status(struct afs_operation *, struct afs_vnode_param *);
 extern int afs_fetch_status(struct afs_vnode *, struct key *, bool, afs_access_t *);
 extern int afs_ilookup5_test_by_fid(struct inode *, void *);

fs/afs/mntpt.c

@@ -30,7 +30,7 @@ const struct file_operations afs_mntpt_file_operations = {
 
 const struct inode_operations afs_mntpt_inode_operations = {
 	.lookup		= afs_mntpt_lookup,
-	.readlink	= page_readlink,
+	.readlink	= afs_readlink,
 	.getattr	= afs_getattr,
 };
 
@@ -118,26 +118,26 @@ static int afs_mntpt_set_params(struct fs_context *fc, struct dentry *mntpt)
 		ctx->volnamesz = sizeof(afs_root_volume) - 1;
 	} else {
 		/* read the contents of the AFS special symlink */
-		struct page *page;
+		DEFINE_DELAYED_CALL(cleanup);
+		const char *content;
 		loff_t size = i_size_read(d_inode(mntpt));
-		char *buf;
 
 		if (src_as->cell)
 			ctx->cell = afs_use_cell(src_as->cell, afs_cell_trace_use_mntpt);
 
 		if (size < 2 || size > PAGE_SIZE - 1)
 			return -EINVAL;
 
-		page = read_mapping_page(d_inode(mntpt)->i_mapping, 0, NULL);
-		if (IS_ERR(page))
-			return PTR_ERR(page);
+		content = afs_get_link(mntpt, d_inode(mntpt), &cleanup);
+		if (IS_ERR(content)) {
+			do_delayed_call(&cleanup);
+			return PTR_ERR(content);
+		}
 
-		buf = kmap(page);
 		ret = -EINVAL;
-		if (buf[size - 1] == '.')
-			ret = vfs_parse_fs_string(fc, "source", buf, size - 1);
-		kunmap(page);
-		put_page(page);
+		if (content[size - 1] == '.')
+			ret = vfs_parse_fs_string(fc, "source", content, size - 1);
+		do_delayed_call(&cleanup);
 		if (ret < 0)
 			return ret;
 

include/trace/events/afs.h

@@ -422,6 +422,7 @@ enum yfs_cm_operation {
 	EM(afs_file_error_dir_over_end,		"DIR_ENT_OVER_END")	\
 	EM(afs_file_error_dir_small,		"DIR_SMALL")		\
 	EM(afs_file_error_dir_unmarked_ext,	"DIR_UNMARKED_EXT")	\
+	EM(afs_file_error_symlink_big,		"SYM_BIG")		\
 	EM(afs_file_error_mntpt,		"MNTPT_READ_FAILED")	\
 	E_(afs_file_error_writeback_fail,	"WRITEBACK_FAILED")