From bc8879f4f5f3bc19f6f87a0b7136fd5297dce628 Mon Sep 17 00:00:00 2001 From: Sergey Bugaev Date: Mon, 6 Nov 2023 16:50:51 +0300 Subject: [PATCH] hurd: Stop mapping AT_NO_AUTOMOUNT to O_NOTRANS While AT_NO_AUTOMOUNT is similar in function to the Hurd's O_NOTRANS, there are significant enough differences in semantics: 1. AT_NO_AUTOMOUNT has no effect on already established mounts, whereas O_NOTRANS causes the lookup to ignore both passive and active translators. A better approximation of the AT_NO_AUTOMOUNT behavior would be to honor active translators, but avoid starting passive ones; like what the file_name_lookup_carefully () routine from sutils/clookup.c in the Hurd source tree does. 2. On GNU/Hurd, translators are used much more pervasively than mounts on "traditional" Unix systems: among other things, translators underlie features like symlinks, device nodes, and sockets. And while on a "traditional" Unix system, the mountpoint and the root of the mounted tree may look similar enough for many purposes (they're both directories, for one thing), the Hurd allows for any combination of the two node types, and indeed it is common to have e.g. a device node "mounted" on top of a regular file node on the underlying filesystem. Ignoring the translator and stat'ing the underlying node is therefore likely to return very different results from what you'd get if you stat the translator's root node. In practice, mapping AT_NO_AUTOMOUNT to O_NOTRANS was breaking GNU Coreutils, including stat(1) and ls(1): $ stat /dev/hd0s1 File: /dev/hd0s1 Size: 0 Blocks: 8 IO Block: 8192 regular empty file Device: 0,8 Inode: 32866 Links: 1 This was also breaking GNOME's glib, where a g_local_file_stat () call that is supposed to stat () a file through a symlink uses AT_NO_AUTOMOUNT, which gets mapped to O_NOTRANS, which then causes the stat () call to stat symlink itself like lstat () would, rather then the file it points to, which is what the logic expects to happen. This reverts most of 13710e7e6af6c8965cc9a63a0660cb4ce1966557 "hurd: Add support for AT_NO_AUTOMOUNT". Signed-off-by: Sergey Bugaev --- hurd/hurd/fd.h | 2 -- 1 file changed, 2 deletions(-) diff --git a/hurd/hurd/fd.h b/hurd/hurd/fd.h index 1616c635d5..7bdb4d0ea9 100644 --- a/hurd/hurd/fd.h +++ b/hurd/hurd/fd.h @@ -300,8 +300,6 @@ __hurd_at_flags (int *at_flags, int *flags) *flags &= ~O_NOLINK; *at_flags &= ~AT_SYMLINK_FOLLOW; - if (*at_flags & AT_NO_AUTOMOUNT) - *flags |= O_NOTRANS; *at_flags &= ~AT_NO_AUTOMOUNT; if (*at_flags != 0)