inode更新access時間

更新檔案的通路時間：      

/**
 *	touch_atime	-	update the access time
 *	@path: the &struct path to update
 *	@inode: inode to update
 *
 *	Update the accessed time on an inode and mark it for writeback.
 *	This function automatically handles read only file systems and media,
 *	as well as the "noatime" flag and inode specific "noatime" markers.
 */
bool __atime_needs_update(const struct path *path, struct inode *inode,
			  bool rcu)
{
	struct vfsmount *mnt = path->mnt;
	struct timespec now;


	if (inode->i_flags & S_NOATIME)
		return false;


	/* Atime updates will likely cause i_uid and i_gid to be written
	 * back improprely if their true value is unknown to the vfs.
	 */
	if (HAS_UNMAPPED_ID(inode))
		return false;


	if (IS_NOATIME(inode))
		return false;
	if ((inode->i_sb->s_flags & MS_NODIRATIME) && S_ISDIR(inode->i_mode))
		return false;


	if (mnt->mnt_flags & MNT_NOATIME)
		return false;
	if ((mnt->mnt_flags & MNT_NODIRATIME) && S_ISDIR(inode->i_mode))
		return false;


	now = current_time(inode);


	if (!relatime_need_update(path, inode, now, rcu))
		return false;


	if (timespec_equal(&inode->i_atime, &now))
		return false;


	return true;
}
      

void touch_atime(const struct path *path)
{
	struct vfsmount *mnt = path->mnt;
	struct inode *inode = d_inode(path->dentry);
	struct timespec now;


	if (!__atime_needs_update(path, inode, false))
		return;


	if (!sb_start_write_trylock(inode->i_sb))
		return;


	if (__mnt_want_write(mnt) != 0)
		goto skip_update;
	/*
	 * File systems can error out when updating inodes if they need to
	 * allocate new space to modify an inode (such is the case for
	 * Btrfs), but since we touch atime while walking down the path we
	 * really don't care if we failed to update the atime of the file,
	 * so just ignore the return value.
	 * We may also fail on filesystems that have the ability to make parts
	 * of the fs read only, e.g. subvolumes in Btrfs.
	 */
	now = current_time(inode);
	update_time(inode, &now, S_ATIME);
	__mnt_drop_write(mnt);
skip_update:
	sb_end_write(inode->i_sb);
}
EXPORT_SYMBOL(touch_atime);