ubifs: introduce UBIFS_ATIME_SUPPORT to ubifs

To make ubifs support atime flexily, this commit introduces
a Kconfig option named as UBIFS_ATIME_SUPPORT.

With UBIFS_ATIME_SUPPORT=n:
	ubifs keeps the full compatibility to no_atime from
the start of ubifs.

=================UBIFS_ATIME_SUPPORT=n=======================
-o - no atime
-o atime - no atime
-o noatime - no atime
-o relatime - no atime
-o strictatime - no atime
-o lazyatime - no atime

With UBIFS_ATIME_SUPPORT=y:
	ubifs supports the atime same with other main stream
file systems.
=================UBIFS_ATIME_SUPPORT=y=======================
-o - default behavior (relatime currently)
-o atime - atime support
-o noatime - no atime support
-o relatime - relative atime support
-o strictatime - strict atime support
-o lazyatime - lazy atime support

Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
Reviewed-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Richard Weinberger <richard@nod.at>

fs/ubifs/Kconfig

@@ -35,3 +35,18 @@ config UBIFS_FS_ZLIB
 	default y
 	help
 	  Zlib compresses better than LZO but it is slower. Say 'Y' if unsure.
+
+config UBIFS_ATIME_SUPPORT
+	bool "Access time support" if UBIFS_FS
+	depends on UBIFS_FS
+	default n
+	help
+	  Originally UBIFS did not support atime, because it looked like a bad idea due
+	  increased flash wear. This option adds atime support and it is disabled by default
+	  to preserve the old behavior. If you enable this option, UBIFS starts updating atime,
+	  which means that file-system read operations will cause writes (inode atime
+	  updates). This may affect file-system performance and increase flash device wear,
+	  so be careful. How often atime is updated depends on the selected strategy:
+	  strictatime is the "heavy", relatime is "lighter", etc.
+
+	  If unsure, say 'N'

fs/ubifs/dir.c

@@ -1186,6 +1186,9 @@ const struct inode_operations ubifs_dir_inode_operations = {
 	.getxattr    = ubifs_getxattr,
 	.listxattr   = ubifs_listxattr,
 	.removexattr = ubifs_removexattr,
+#ifdef CONFIG_UBIFS_ATIME_SUPPORT
+	.update_time = ubifs_update_time,
+#endif
 };
 
 const struct file_operations ubifs_dir_operations = {

fs/ubifs/file.c

@@ -1354,6 +1354,47 @@ static inline int mctime_update_needed(const struct inode *inode,
 	return 0;
 }
 
+#ifdef CONFIG_UBIFS_ATIME_SUPPORT
+/**
+ * ubifs_update_time - update time of inode.
+ * @inode: inode to update
+ *
+ * This function updates time of the inode.
+ */
+int ubifs_update_time(struct inode *inode, struct timespec *time,
+			     int flags)
+{
+	struct ubifs_inode *ui = ubifs_inode(inode);
+	struct ubifs_info *c = inode->i_sb->s_fs_info;
+	struct ubifs_budget_req req = { .dirtied_ino = 1,
+			.dirtied_ino_d = ALIGN(ui->data_len, 8) };
+	int iflags = I_DIRTY_TIME;
+	int err, release;
+
+	err = ubifs_budget_space(c, &req);
+	if (err)
+		return err;
+
+	mutex_lock(&ui->ui_mutex);
+	if (flags & S_ATIME)
+		inode->i_atime = *time;
+	if (flags & S_CTIME)
+		inode->i_ctime = *time;
+	if (flags & S_MTIME)
+		inode->i_mtime = *time;
+
+	if (!(inode->i_sb->s_flags & MS_LAZYTIME))
+		iflags |= I_DIRTY_SYNC;
+
+	release = ui->dirty;
+	__mark_inode_dirty(inode, iflags);
+	mutex_unlock(&ui->ui_mutex);
+	if (release)
+		ubifs_release_budget(c, &req);
+	return 0;
+}
+#endif
+
 /**
  * update_ctime - update mtime and ctime of an inode.
  * @inode: inode to update
@@ -1537,6 +1578,9 @@ static int ubifs_file_mmap(struct file *file, struct vm_area_struct *vma)
 	if (err)
 		return err;
 	vma->vm_ops = &ubifs_file_vm_ops;
+#ifdef CONFIG_UBIFS_ATIME_SUPPORT
+	file_accessed(file);
+#endif
 	return 0;
 }
 
@@ -1557,6 +1601,9 @@ const struct inode_operations ubifs_file_inode_operations = {
 	.getxattr    = ubifs_getxattr,
 	.listxattr   = ubifs_listxattr,
 	.removexattr = ubifs_removexattr,
+#ifdef CONFIG_UBIFS_ATIME_SUPPORT
+	.update_time = ubifs_update_time,
+#endif
 };
 
 const struct inode_operations ubifs_symlink_inode_operations = {
@@ -1568,6 +1615,9 @@ const struct inode_operations ubifs_symlink_inode_operations = {
 	.getxattr    = ubifs_getxattr,
 	.listxattr   = ubifs_listxattr,
 	.removexattr = ubifs_removexattr,
+#ifdef CONFIG_UBIFS_ATIME_SUPPORT
+	.update_time = ubifs_update_time,
+#endif
 };
 
 const struct file_operations ubifs_file_operations = {

fs/ubifs/super.c

@@ -128,7 +128,10 @@ struct inode *ubifs_iget(struct super_block *sb, unsigned long inum)
 	if (err)
 		goto out_ino;
 
-	inode->i_flags |= (S_NOCMTIME | S_NOATIME);
+	inode->i_flags |= S_NOCMTIME;
+#ifndef CONFIG_UBIFS_ATIME_SUPPORT
+	inode->i_flags |= S_NOATIME;
+#endif
 	set_nlink(inode, le32_to_cpu(ino->nlink));
 	i_uid_write(inode, le32_to_cpu(ino->uid));
 	i_gid_write(inode, le32_to_cpu(ino->gid));
@@ -2139,7 +2142,12 @@ static struct dentry *ubifs_mount(struct file_system_type *fs_type, int flags,
 		if (err)
 			goto out_deact;
 		/* We do not support atime */
-		sb->s_flags |= MS_ACTIVE | MS_NOATIME;
+		sb->s_flags |= MS_ACTIVE;
+#ifndef CONFIG_UBIFS_ATIME_SUPPORT
+		sb->s_flags |= MS_NOATIME;
+#else
+		ubifs_msg(c, "full atime support is enabled.");
+#endif
 	}
 
 	/* 'fill_super()' opens ubi again so we must close it here */

fs/ubifs/ubifs.h

@@ -1746,6 +1746,9 @@ int ubifs_calc_dark(const struct ubifs_info *c, int spc);
 /* file.c */
 int ubifs_fsync(struct file *file, loff_t start, loff_t end, int datasync);
 int ubifs_setattr(struct dentry *dentry, struct iattr *attr);
+#ifdef CONFIG_UBIFS_ATIME_SUPPORT
+int ubifs_update_time(struct inode *inode, struct timespec *time, int flags);
+#endif
 
 /* dir.c */
 struct inode *ubifs_new_inode(struct ubifs_info *c, const struct inode *dir,