On Tue, Aug 27, 2013 at 4:08 PM, Al Viro <v...@zeniv.linux.org.uk> wrote:
> On Tue, Aug 27, 2013 at 12:16:34PM -0700, Andy Lutomirski 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).
>>
>> The basic idea is that there's a new helper function
>> user_file_or_path_at. It takes an fd and a path and, depending on
>> flags, the emptiness of the path, and whether path is a magic /proc
>> symlink (or a symlink to a magic /proc/symlink), it returns either a
>> struct path or a struct file *.
>
> No.
I'm curious what's wrong with the general concept. (I agree that the
implementation is heinous.)
If I ever wanted to add a new *at syscall, I'd like to be able to do:
int sys_whateverat(int dfd, const char __user *name, int flags)
{
resolve_the_thing(dfd, name, flags);
if (it's a file) {
check fmode;
} else {
inode_permission();
}
actually_do_something(inode);
unreference_whatever_i_got();
return ret;
}
thereby killing the fwhatever and whateverat birds with one stone.
>
>> + path_get(&nd->path);
>> + if (nd->flags & LOOKUP_FILE) {
>> + if (nd->last_symlink_file)
>> + fput(nd->last_symlink_file);
>> + nd->last_symlink_file = file;
>
> This is ugly (and costs quite a bit of overhead)
>
>> -static int proc_cwd_link(struct dentry *dentry, struct path *path)
>> +static int proc_cwd_link(struct dentry *dentry, struct file_or_path *link)
>
> ... and this is even more vile. Vetoed, for being too ugly to live.
...phew. I wasn't looking forward to testing and debugging my crap :)
--Andy
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