Shun-ichi GOTO wrote:
>
> >>>>> at Tue, 13 Nov 2001 21:58:32 -0600
> >>>>> Randy Reitz <[EMAIL PROTECTED]> said,>
>
> > Here is a test program....
>
> It's strange test.
> Do like this, and get result: "2nd write() failed: Bad address".
> So you should give valid pointer as 2nd argument of 2nd write() call.
> for example, write (fd, buf, 0);
>
It's not so strange if you think about it :) If a length of 0 is given
there is no reason to check the pointer for being valid IMO.
However here is what the linux man page says about write - havent
checked
any other source which may be more confident though:
RETURN VALUE
On success, the number of bytes written are returned (zero
indicates nothing was written).
On error, -1 is returned, and errno is set appropriately. If
count is zero and the file
descriptor refers to a regular file, 0 will be returned without
causing any other effect.
For a special file, the results are not portable.
So at least linux just checks for valid fd when the len is 0.
And the testcase which Randy posted is just fine when run on Linux of
course
if the file exists.
[ptsekov@enigma Src]$ ~/Src/write_test
ret=0, errno=0
If the file does not exists at the time the testcase is run i get:
[ptsekov@enigma Src]$ ~/Src/write_test
ret=-1, errno=9 (Bad file descriptor)
Attached is a simple patch which moves the buffer check after the
check for valid file descriptor and the check for zero len.
2001-11-14 Pavel Tsekov <[EMAIL PROTECTED]>
* syscalls.cc (_write): Check if the third argument of _write() is zero.
If the first argument of _write() is a valid file descriptor and the
third
argument is zero - return 0 without doing anything else.
Perform a validation check on the second argument of _write() only if
the
_write() is requested on a valid file descriptor and the length of the
buffer being written is not zero.
--- syscalls.cc.ORIG Wed Nov 14 10:33:03 2001
+++ syscalls.cc Wed Nov 14 10:36:41 2001
@@ -355,15 +355,21 @@ _read (int fd, void *ptr, size_t len)
extern "C" ssize_t
_write (int fd, const void *ptr, size_t len)
{
- if (__check_invalid_read_ptr_errno (ptr, len))
- return -1;
-
int res = -1;
sigframe thisframe (mainthread);
cygheap_fdget cfd (fd);
if (cfd < 0)
goto done;
+
+ if (len == 0)
+ {
+ res = 0;
+ goto done;
+ }
+
+ if (__check_invalid_read_ptr_errno (ptr, len))
+ return -1;
/* Could block, so let user know we at least got here. */
if (fd == 1 || fd == 2)
--
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