[PATCH v2 35/53] cachefiles: Implement a function to get/create a directory in the cache

[David Howells <dhowells@xxxxxxxxxx>]

Implement a function to get/create structural directories in the cache.
This is used for setting up a cache and creating volume substructures.

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: linux-cachefs@xxxxxxxxxx
---

 fs/cachefiles/Makefile   |    3 +
 fs/cachefiles/internal.h |    7 ++
 fs/cachefiles/namei.c    |  133 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 142 insertions(+), 1 deletion(-)
 create mode 100644 fs/cachefiles/namei.c

diff --git a/fs/cachefiles/Makefile b/fs/cachefiles/Makefile
index 4c80d9af151f..06a87f78b88c 100644
--- a/fs/cachefiles/Makefile
+++ b/fs/cachefiles/Makefile
@@ -5,7 +5,8 @@
 
 cachefiles-y := \
 	daemon.o \
-	main.o
+	main.o \
+	namei.o
 
 cachefiles-$(CONFIG_CACHEFILES_ERROR_INJECTION) += error_inject.o
 
diff --git a/fs/cachefiles/internal.h b/fs/cachefiles/internal.h
index 3ccc8411c502..4e77c3004d98 100644
--- a/fs/cachefiles/internal.h
+++ b/fs/cachefiles/internal.h
@@ -168,6 +168,13 @@ static inline int cachefiles_inject_remove_error(void)
 	return cachefiles_error_injection_state & 2 ? -EIO : 0;
 }
 
+/*
+ * namei.c
+ */
+extern struct dentry *cachefiles_get_directory(struct cachefiles_cache *cache,
+					       struct dentry *dir,
+					       const char *name);
+
 /*
  * error handling
  */
diff --git a/fs/cachefiles/namei.c b/fs/cachefiles/namei.c
new file mode 100644
index 000000000000..69915dde0a83
--- /dev/null
+++ b/fs/cachefiles/namei.c
@@ -0,0 +1,133 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* CacheFiles path walking and related routines
+ *
+ * Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@xxxxxxxxxx)
+ */
+
+#include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/file.h>
+#include <linux/fs.h>
+#include <linux/fsnotify.h>
+#include <linux/quotaops.h>
+#include <linux/xattr.h>
+#include <linux/mount.h>
+#include <linux/namei.h>
+#include <linux/security.h>
+#include <linux/slab.h>
+#include "internal.h"
+
+/*
+ * get a subdirectory
+ */
+struct dentry *cachefiles_get_directory(struct cachefiles_cache *cache,
+					struct dentry *dir,
+					const char *dirname)
+{
+	struct dentry *subdir;
+	struct path path;
+	int ret;
+
+	_enter(",,%s", dirname);
+
+	/* search the current directory for the element name */
+	inode_lock(d_inode(dir));
+
+retry:
+	ret = cachefiles_inject_read_error();
+	if (ret == 0)
+		subdir = lookup_one_len(dirname, dir, strlen(dirname));
+	else
+		subdir = ERR_PTR(ret);
+	if (IS_ERR(subdir)) {
+		trace_cachefiles_vfs_error(NULL, d_backing_inode(dir),
+					   PTR_ERR(subdir),
+					   cachefiles_trace_lookup_error);
+		if (PTR_ERR(subdir) == -ENOMEM)
+			goto nomem_d_alloc;
+		goto lookup_error;
+	}
+
+	_debug("subdir -> %pd %s",
+	       subdir, d_backing_inode(subdir) ? "positive" : "negative");
+
+	/* we need to create the subdir if it doesn't exist yet */
+	if (d_is_negative(subdir)) {
+		if (cache->store) {
+			ret = cachefiles_has_space(cache, 1, 0);
+			if (ret < 0)
+				goto mkdir_error;
+		}
+
+		_debug("attempt mkdir");
+
+		path.mnt = cache->mnt;
+		path.dentry = dir;
+		ret = security_path_mkdir(&path, subdir, 0700);
+		if (ret < 0)
+			goto mkdir_error;
+		ret = cachefiles_inject_write_error();
+		if (ret == 0)
+			ret = vfs_mkdir(&init_user_ns, d_inode(dir), subdir, 0700);
+		if (ret < 0) {
+			trace_cachefiles_vfs_error(NULL, d_inode(dir), ret,
+						   cachefiles_trace_mkdir_error);
+			goto mkdir_error;
+		}
+
+		if (unlikely(d_unhashed(subdir))) {
+			dput(subdir);
+			goto retry;
+		}
+		ASSERT(d_backing_inode(subdir));
+
+		_debug("mkdir -> %pd{ino=%lu}",
+		       subdir, d_backing_inode(subdir)->i_ino);
+	}
+
+	inode_unlock(d_inode(dir));
+
+	/* we need to make sure the subdir is a directory */
+	ASSERT(d_backing_inode(subdir));
+
+	if (!d_can_lookup(subdir)) {
+		pr_err("%s is not a directory\n", dirname);
+		ret = -EIO;
+		goto check_error;
+	}
+
+	ret = -EPERM;
+	if (!(d_backing_inode(subdir)->i_opflags & IOP_XATTR) ||
+	    !d_backing_inode(subdir)->i_op->lookup ||
+	    !d_backing_inode(subdir)->i_op->mkdir ||
+	    !d_backing_inode(subdir)->i_op->rename ||
+	    !d_backing_inode(subdir)->i_op->rmdir ||
+	    !d_backing_inode(subdir)->i_op->unlink)
+		goto check_error;
+
+	_leave(" = [%lu]", d_backing_inode(subdir)->i_ino);
+	return subdir;
+
+check_error:
+	dput(subdir);
+	_leave(" = %d [check]", ret);
+	return ERR_PTR(ret);
+
+mkdir_error:
+	inode_unlock(d_inode(dir));
+	dput(subdir);
+	pr_err("mkdir %s failed with error %d\n", dirname, ret);
+	return ERR_PTR(ret);
+
+lookup_error:
+	inode_unlock(d_inode(dir));
+	ret = PTR_ERR(subdir);
+	pr_err("Lookup %s failed with error %d\n", dirname, ret);
+	return ERR_PTR(ret);
+
+nomem_d_alloc:
+	inode_unlock(d_inode(dir));
+	_leave(" = -ENOMEM");
+	return ERR_PTR(-ENOMEM);
+}