(call-process ...) hangs in emacs

Corinna Vinschen corinna-cygwin@cygwin.com
Thu Aug 28 10:01:00 GMT 2014


On Aug 28 01:02, Andrey Repin wrote:
> Greetings, Corinna Vinschen!
> 
> > faccessat/access/eaccess don't try to be intelligent by themselves.
> > Rather they just call a Windows function if the filesystem is mounted
> > with "acl" mount flags:
> 
> > - Fetch file's security descriptor
> > - Create process impersonation token.
> > - Call NtAccessCheck
> > - If NtAccessCheck returns "not allowed", check for backup/restore
> >   privileges via NtPrivilegeCheck.
> 
> > In "noacl" mode or on filesystems not supporting ACLs, access uses the
> > st_mode flags from stat() to figure out the permissions.
> 
> I'm not very much into Cygwin internals, so beg pardon if I got something
> wrong here... But reading this makes my internal sanity checker go into red
> alarm state.
> 
> Here's why:
> 
> When Cygwin mount a filesystem with 'acl' flag set, it mangles current ACL's
> set on the files to produce something that can be understood as basic POSIX
> 'ugly'...erm, 'ugo' permissions. Behavior least desirable in many cases.
> You say, it will then use native functions to determine access rights... No
> wonder they will work, since you already mangled them to suit your needs.
> 
> When Cygwin mount a filesystem with 'noacl' flag, thus let OS use true ACL's
> (a feature Windows implemented surprisingly fast, while *NIX was only
> proposing it... for far too long without any result in sight), it is then
> followed by some magic and guesswork on Cygwin's end to find out access
> rights.
> 
> If you ask me, something isn't quite right here. Or something is missing.

It's what "acl" means on Cygwin.  "acl" means that Windowsd ACLs are used
and permissions are handled and converted to and from POSIX permissions.
"noacl" means, Cygwin ignores all ACLs and fakes ownership and POSIX
permissions only based only on filetype and DOS R/O attribute, as it has
to on filesystems not supporting ACLs, like FAT/FAT32.


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat
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