[re-adding Ralf, in case he's not subscribed] On 02/02/2011 02:53 PM, Corinna Vinschen wrote: >> No, I'm using tcsh. Apparently you're right, it doesn't work in >> XP, but it works in W7. Looks like Microsoft reworked the CreateProcess >> call at some point. I have an idea how this might be possible to >> workaround. Stay tuned. > > Yes, my workaround works. What happens is that XP's CreateProcess calls > an internal function at one point which drops leading spaces and > trailing dots and spaces from the path, since these were always invalid > in DOS paths. And a path component which consists entirely of dots > and/or spaces is just invisible from a DOS path perspective. > > However, if the path to the executable is prepended by the long-path > prefix "\\?\", then the CreateProcess function understands the path > even on XP since the prefix suppresses the DOS path strangling. > > However, that's not a generic solution. At one point we deliberately > dropped the preceeding "\\?\" because this breaks some native Win32 > child processes which are not long-path aware. So, right now, we only > keep the long-path prefix if the path is actually longer than MAX_PATH. > > To fix that, we would have to scan the entire path for path components > which contain leading spaces or trailing dots or spaces. That makes > fork even slower than it already is.
Well, that would only be if the path is shorter than MAX_PATH (256) bytes, so it's not like we have a quadratic scaling problem over thousands of bytes. Furthermore, using a directory literally named '...' already causes problems for windows programs that ar not long-path aware, so the workaround is no worse than what they currently get from such a path. But you're right, that taking the time to scan for any occurrence of: '.\', './', '/.', ' \', ' /' and checking for five patterns across 256 bytes definitely adds time. > Given that it works fine on Vista and Windows 7 anyway, is it really > worth to add this extra code just to support an old OS in a very rare > situation? Can't we make the scan conditional on the windows version? That is, spend the extra time to keep XP happy, but skip the scan on newer Windows? -- Eric Blake ebl...@redhat.com +1-801-349-2682 Libvirt virtualization library http://libvirt.org
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