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 13710e7e6a
"hurd: Add support for AT_NO_AUTOMOUNT".
Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
bc8879f4f5