Messages in this thread | | | From | Andy Lutomirski <> | Date | Tue, 27 Aug 2013 13:28:27 -0700 | Subject | Re: [RFC PATCH] fs: Add user_file_or_path_at and use it for truncate |
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On Tue, Aug 27, 2013 at 12:32 PM, Linus Torvalds <torvalds@linux-foundation.org> wrote: > On Tue, Aug 27, 2013 at 12:16 PM, Andy Lutomirski <luto@amacapital.net> wrote: >> This is an experiment to see if we can get nice semantics for all syscalls >> that either follow symlinks or allow AT_EMPTY_PATH without jumping through >> enormous hoops. This converts truncate (although you can't tell using >> truncate from coreutils, because it actually uses open + ftruncate). > > So this seems *way* too complex. I'd much rather see "nd->flags" get a > LOOKUP_READONLY flag, for example, that gets set by > proc_pid_follow_link() when it hits a read-only file descriptor (and > gets cleared by other lookups). > > Wouldn't that be *much* more straightforward?
It would if it works. It certainly would for truncate, setxattr, etc.
There are funny cases, though. For example, execing an O_WRONLY fd should probably fail, as should opening an O_WRONLY fd as O_RDWR. O_APPEND is also funny. flink will (I suspect) always want to be a bit special.
There are also O_PATH fds, and I'm not sure what the semantics of O_PATH fds are or should be when they refer to something other than a directory.
The benefit of my approach is that it's really obvious that truncate("/proc/self/fd/N") and ftruncate(N) do exactly the same thing. The downside is that the namei code is a bit gross and there was more rearranging of ftruncate than I would have liked. (I also lost the benefit of fget_light, but I could fix that by passing a struct fd around instead of a struct file *.)
--Andy
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