On Fri, Nov 17, 2017 at 12:03 AM, Vivek Goyal <vgoyal@xxxxxxxxxx> wrote: > d_real() can make a upper metacopy dentry/inode visible to the vfs layer. > This is something new and vfs layer does not know that this inode contains > only metadata and not data. And this could break things. > > So to be safe, do not expose metacopy only dentry/inode to vfs using d_real(). > > For regular d_real() call (inode == NULL, D_REAL_UPPER not set), if upper > dentry inode is metacopy only and does not have data, return lower dentry. > > If d_real() is called with flag D_REAL_UPPER, return upper dentry only if > it has data (flag OVL_UPPERDATA is set). > > Similiarly, if d_real(inode=X) is called, a warning is emitted if returned > dentry/inode does not have OVL_UPPERDATA set. This should not happen as > we never made this metacopy inode visible to vfs so nobody should be calling > overlayfs back with inode=metacopy_inode. > > I scanned the code and I don't think it breaks any of the existing code. > There are two users of D_REAL_UPPER. may_write_real() and > update_ovl_inode_times(). > > may_write_real(), will get an NULL dentry if upper inode is metacopy only > and it will return -EPERM. Effectively, we are disallowing modifications > to metacopy only inode from this interface. Though there is opportunity > to improve it. (Allow chattr on metacopy inodes). > > update_ovl_inode_times() gets inode mtime and ctime from real inode. It > should not be broken for metacopy inode as well for following reasons. > > > - For any metadata operations (setattr, acl etc), overlay always calls > ovl_copyattr() and updates ovl inode mtime and ctime. So there is no > need to update mtime and ctime int his case. Its already updated. > > - For metadata inode, mtime should be same as lower and not change. (data > can't be modified on metadata inode without copyup). > > - For file writes, ctime and mtime will be updated. But in that case > first data will be copied up and this will not be a metadata inode > anymore. And furthr call to d_real(D_REAL_UPPER) will return upper > inode and new mtime and ctime will be obtainable. > > So atime updates should work just fine for metacopy inodes. > > Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx> Reviewed-by: Amir Goldstein <amir73il@xxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-unionfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
