fscache, cachefiles: Store the volume coherency data

Store the volume coherency data in an xattr and check it when we rebind the
volume.  If it doesn't match the cache volume is moved to the graveyard and
rebuilt anew.

Changes
=======
ver #4:
 - Remove a couple of debugging prints.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Link: https://lore.kernel.org/r/163967164397.1823006.2950539849831291830.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021563138.640689.15851092065380543119.stgit@warthog.procyon.org.uk/ # v4

3 files changed, 103 insertions, 2 deletions

diff --git a/fs/cachefiles/internal.h b/fs/cachefiles/internal.h
index d5868f5514d3..abdd1b66f6b9 100644
--- a/fs/cachefiles/internal.h
+++ b/fs/cachefiles/internal.h
@@ -270,6 +270,8 @@ extern int cachefiles_remove_object_xattr(struct cachefiles_cache *cache,
 					  struct cachefiles_object *object,
 					  struct dentry *dentry);
 extern void cachefiles_prepare_to_write(struct fscache_cookie *cookie);
+extern bool cachefiles_set_volume_xattr(struct cachefiles_volume *volume);
+extern int cachefiles_check_volume_xattr(struct cachefiles_volume *volume);
 
 /*
  * Error handling
diff --git a/fs/cachefiles/volume.c b/fs/cachefiles/volume.c
index 4a14f5e72764..89df0ba8ba5e 100644
--- a/fs/cachefiles/volume.c
+++ b/fs/cachefiles/volume.c
@@ -22,7 +22,8 @@ void cachefiles_acquire_volume(struct fscache_volume *vcookie)
 	struct dentry *vdentry, *fan;
 	size_t len;
 	char *name;
-	int n_accesses, i;
+	bool is_new = false;
+	int ret, n_accesses, i;
 
 	_enter("");
 
@@ -43,11 +44,29 @@ void cachefiles_acquire_volume(struct fscache_volume *vcookie)
 	memcpy(name + 1, vcookie->key + 1, len);
 	name[len + 1] = 0;
 
-	vdentry = cachefiles_get_directory(cache, cache->store, name, NULL);
+retry:
+	vdentry = cachefiles_get_directory(cache, cache->store, name, &is_new);
 	if (IS_ERR(vdentry))
 		goto error_name;
 	volume->dentry = vdentry;
 
+	if (is_new) {
+		if (!cachefiles_set_volume_xattr(volume))
+			goto error_dir;
+	} else {
+		ret = cachefiles_check_volume_xattr(volume);
+		if (ret < 0) {
+			if (ret != -ESTALE)
+				goto error_dir;
+			inode_lock_nested(d_inode(cache->store), I_MUTEX_PARENT);
+			cachefiles_bury_object(cache, NULL, cache->store, vdentry,
+					       FSCACHE_VOLUME_IS_WEIRD);
+			cachefiles_put_directory(volume->dentry);
+			cond_resched();
+			goto retry;
+		}
+	}
+	
 	for (i = 0; i < 256; i++) {
 		sprintf(name, "@%02x", i);
 		fan = cachefiles_get_directory(cache, vdentry, name, NULL);
@@ -74,6 +93,7 @@ void cachefiles_acquire_volume(struct fscache_volume *vcookie)
 error_fan:
 	for (i = 0; i < 256; i++)
 		cachefiles_put_directory(volume->fanout[i]);
+error_dir:
 	cachefiles_put_directory(volume->dentry);
 error_name:
 	kfree(name);
@@ -114,5 +134,6 @@ void cachefiles_free_volume(struct fscache_volume *vcookie)
 void cachefiles_withdraw_volume(struct cachefiles_volume *volume)
 {
 	fscache_withdraw_volume(volume->vcookie);
+	cachefiles_set_volume_xattr(volume);
 	__cachefiles_free_volume(volume);
 }
diff --git a/fs/cachefiles/xattr.c b/fs/cachefiles/xattr.c
index 0601c46a22ef..83f41bd0c3a9 100644
--- a/fs/cachefiles/xattr.c
+++ b/fs/cachefiles/xattr.c
@@ -179,3 +179,81 @@ void cachefiles_prepare_to_write(struct fscache_cookie *cookie)
 		cachefiles_end_secure(cache, saved_cred);
 	}
 }
+
+/*
+ * Set the state xattr on a volume directory.
+ */
+bool cachefiles_set_volume_xattr(struct cachefiles_volume *volume)
+{
+	unsigned int len = volume->vcookie->coherency_len;
+	const void *p = volume->vcookie->coherency;
+	struct dentry *dentry = volume->dentry;
+	int ret;
+
+	_enter("%x,#%d", volume->vcookie->debug_id, len);
+
+	ret = cachefiles_inject_write_error();
+	if (ret == 0)
+		ret = vfs_setxattr(&init_user_ns, dentry, cachefiles_xattr_cache,
+				   p, len, 0);
+	if (ret < 0) {
+		trace_cachefiles_vfs_error(NULL, d_inode(dentry), ret,
+					   cachefiles_trace_setxattr_error);
+		trace_cachefiles_vol_coherency(volume, d_inode(dentry)->i_ino,
+					       cachefiles_coherency_vol_set_fail);
+		if (ret != -ENOMEM)
+			cachefiles_io_error(
+				volume->cache, "Failed to set xattr with error %d", ret);
+	} else {
+		trace_cachefiles_vol_coherency(volume, d_inode(dentry)->i_ino,
+					       cachefiles_coherency_vol_set_ok);
+	}
+
+	_leave(" = %d", ret);
+	return ret == 0;
+}
+
+/*
+ * Check the consistency between the backing cache and the volume cookie.
+ */
+int cachefiles_check_volume_xattr(struct cachefiles_volume *volume)
+{
+	struct cachefiles_xattr *buf;
+	struct dentry *dentry = volume->dentry;
+	unsigned int len = volume->vcookie->coherency_len;
+	const void *p = volume->vcookie->coherency;
+	enum cachefiles_coherency_trace why;
+	ssize_t xlen;
+	int ret = -ESTALE;
+
+	_enter("");
+
+	buf = kmalloc(len, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
+	xlen = cachefiles_inject_read_error();
+	if (xlen == 0)
+		xlen = vfs_getxattr(&init_user_ns, dentry, cachefiles_xattr_cache, buf, len);
+	if (xlen != len) {
+		if (xlen < 0) {
+			trace_cachefiles_vfs_error(NULL, d_inode(dentry), xlen,
+						   cachefiles_trace_getxattr_error);
+			if (xlen == -EIO)
+				cachefiles_io_error(
+					volume->cache,
+					"Failed to read xattr with error %zd", xlen);
+		}
+		why = cachefiles_coherency_vol_check_xattr;
+	} else if (memcmp(buf->data, p, len) != 0) {
+		why = cachefiles_coherency_vol_check_cmp;
+	} else {
+		why = cachefiles_coherency_vol_check_ok;
+		ret = 0;
+	}
+
+	trace_cachefiles_vol_coherency(volume, d_inode(dentry)->i_ino, why);
+	kfree(buf);
+	_leave(" = %d", ret);
+	return ret;
+}