[PATCH] QueryDosDevice in handle_to_fn
Corinna Vinschen
corinna-cygwin@cygwin.com
Sun Mar 16 15:22:00 GMT 2008
On Mar 16 03:14, Brian Dessent wrote:
> I debugged this and found the
> strangest thing, when you call QueryDosDevice (NULL, fnbuf, len) to get
> the list of all DOS devices and len >= 65536, Win32 always returns 0
> with GetLastError set to ERROR_MORE_DATA. Since len was being set as
> "sizeof (OBJECT_NAME_INFORMATION) + NT_MAX_PATH * sizeof (WCHAR)" this
> always happened, causing handle_to_fn() to simply give up and copy the
> Win32 name into the POSIX name and return. The attached patch fixes the
> problem by just clamping the size of the buffer to under 64k.
<insert lament here>
> Another observation that I had while debugging this is that calling
> strncasematch() in this function is probably wrong -- it expands to
> cygwin_strncasecmp(), which is a wrapper that first converts both
> arguments to temporary UNICODE strings and then calls
> RtlCompareUnicodeString() -- we're doing this on strings that we had
> just converted *out* of UNICODE. I think ascii_strncasematch() is
> probably what we want here instead, either that or try to stay in
> unicode throughout.
Using ascii_strncasematch here is right because the DEVICE_PREFIX is
plain ascii anyway. But, yes, the function should be converted to
do everything in WCHAR/UNICODE_STRING and only convert to char *
when creating the final posix_fn.
> + /* For some reason QueryDosDevice will fail with Win32 errno 234
> + (ERROR_MORE_DATA) if you try to pass a buffer larger than 64k */
> + size_t qddlen = len < 65536 ? len : 65535;
len is a const value. Checking len for being < 65536 is a constant
expression which always results in qddlen being 65535 so the ?: is
a noop, more or less.
Did you test if QueryDosDeviceW has the same problem as QueryDosDeviceA?
If not, we should use that function.
Corinna
--
Corinna Vinschen Please, send mails regarding Cygwin to
Cygwin Project Co-Leader cygwin AT cygwin DOT com
Red Hat
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