Mail Archives: cygwin/2001/11/15/06:54:44
There was no feedback on this so I post again :) Is this
cygwin behaviour the expected behaviour ?
Pavel Tsekov wrote:
>
> Shun-ichi GOTO wrote:
> >
> > >>>>> at Tue, 13 Nov 2001 21:58:32 -0600
> > >>>>> Randy Reitz <rreitz AT mssinternet DOT com> 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 AT 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 AT 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 <ptsekov AT syntrex DOT com>
>
> * 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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