On Mon, Dec 28, 2020 at 08:25:50AM -0500, Jeff Layton wrote: > To be clear, the main thing you'll lose with the method above is the > ability to see an unseen error on a newly opened fd, if there was an > overlayfs mount using the same upper sb before your open occurred. > > IOW, consider two overlayfs mounts using the same upper layer sb: > > ovlfs1 ovlfs2 > ---------------------------------------------------------------------- > mount > open fd1 > write to fd1 > <writeback fails> > mount (upper errseq_t SEEN flag marked) > open fd2 > syncfs(fd2) > syncfs(fd1) > > > On a "normal" (non-overlay) fs, you'd get an error back on both syncfs > calls. The first one has a sample from before the error occurred, and > the second one has a sample of 0, due to the fact that the error was > unseen at open time. > > On overlayfs, with the intervening mount of ovlfs2, syncfs(fd1) will > return an error and syncfs(fd2) will not. If we split the SEEN flag into > two, then we can ensure that they both still get an error in this > situation. But do we need to? If the inode has been evicted we also lose the errno. The guarantee we provide is that a fd that was open before the error occurred will see the error. An fd that's opened after the error occurred may or may not see the error.
