From: "H.J. Lu" <hjl.tools@gmail.com>
To: Florian Weimer <fweimer@redhat.com>
Cc: Andreas Schwab <schwab@linux-m68k.org>,
Adhemerval Zanella <adhemerval.zanella@linaro.org>,
Zack Weinberg <zackw@panix.com>,
Siddhesh Poyarekar <siddhesh@gotplt.org>,
GNU C Library <libc-alpha@sourceware.org>
Subject: Re: [PATCH v3 2/2] posix: Implement preadv2 and pwritev2
Date: Sat, 03 Jun 2017 11:27:00 -0000 [thread overview]
Message-ID: <CAMe9rOqPfbjYPgEqmkWEAht+ZzGZk4wikhVCejUuMWtTdQjr8w@mail.gmail.com> (raw)
In-Reply-To: <e6d26a42-f5d2-bada-d44a-42e58b4d1543@redhat.com>
On Sat, Jun 3, 2017 at 4:23 AM, Florian Weimer <fweimer@redhat.com> wrote:
> On 06/03/2017 01:04 PM, H.J. Lu wrote:
>> On Sat, Jun 3, 2017 at 1:22 AM, Andreas Schwab <schwab@linux-m68k.org> wrote:
>>> On Jun 02 2017, "H.J. Lu" <hjl.tools@gmail.com> wrote:
>>>
>>>> The x86-64 LO_HI_LONG can't be used for p{readv,writev}{64}v2. Add a
>>>> new macro, LO_HI_LONG_FLAGS, to pass the off{64}_t and flags arguments.
>>>
>>> Why can't LO_HI_LONG just pass the padding unconditionally on x86_64?
>>>
>>
>> To avoid the unnecessary (long) (((uint64_t) (val)) >> 32).
>
> I think the question is why you can't define it like this:
>
> (val), 0
>
> ? Are you concerned about the additional overhead of passing that
> unnecessary zero at the end of the parameter list for other system
> calls? Or would this result in an observable kernel interface
> difference and break stuff?
My patch has
ndex 7b8bd79..a3fe2fa 100644
--- a/sysdeps/unix/sysv/linux/x86_64/sysdep.h
+++ b/sysdeps/unix/sysv/linux/x86_64/sysdep.h
@@ -389,4 +389,9 @@
#undef LO_HI_LONG
#define LO_HI_LONG(val) (val)
+/* Provide a macro to pass the off{64}_t and flags arguments on
+ p{readv,writev}{64}v2. */
+#undef LO_HI_LONG_FLAGS
+#define LO_HI_LONG_FLAGS(val, flags) (val), 0, (flags)
+
#endif /* linux/x86_64/sysdep.h */
For LO_HI_LONG, it doesn't mater what the second one is. It makes
no difference if -1 is passed. Why bother with 0?
--
H.J.
next prev parent reply other threads:[~2017-06-03 11:27 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-04 12:43 [PATCH v2 1/2] manual: Add preadv and pwritev documentation Adhemerval Zanella
2017-05-04 12:43 ` [PATCH v3 2/2] posix: Implement preadv2 and pwritev2 Adhemerval Zanella
2017-05-11 19:02 ` Adhemerval Zanella
2017-05-30 14:19 ` Adhemerval Zanella
2017-05-31 18:51 ` Adhemerval Zanella
2017-06-01 16:40 ` Siddhesh Poyarekar
2017-06-01 18:14 ` Adhemerval Zanella
2017-06-02 13:00 ` H.J. Lu
2017-06-02 13:04 ` Zack Weinberg
2017-06-02 13:34 ` Florian Weimer
2017-06-02 14:07 ` Adhemerval Zanella
2017-06-02 14:22 ` Zack Weinberg
2017-06-02 18:20 ` Adhemerval Zanella
2017-06-02 19:02 ` Florian Weimer
2017-06-02 19:46 ` Adhemerval Zanella
2017-06-03 1:47 ` H.J. Lu
2017-06-03 8:22 ` Andreas Schwab
2017-06-03 11:04 ` H.J. Lu
2017-06-03 11:23 ` Florian Weimer
2017-06-03 11:27 ` H.J. Lu [this message]
2017-06-03 11:29 ` H.J. Lu
2017-06-03 12:52 ` Andreas Schwab
2017-06-03 12:57 ` H.J. Lu
2017-06-03 13:48 ` Zack Weinberg
2017-06-03 13:52 ` H.J. Lu
2017-06-03 13:58 ` Zack Weinberg
2017-06-03 14:16 ` H.J. Lu
2017-06-03 15:28 ` Andreas Schwab
2017-06-04 13:42 ` H.J. Lu
2017-06-04 15:03 ` Zack Weinberg
2017-06-05 13:37 ` Adhemerval Zanella
2017-06-02 13:04 ` Tulio Magno Quites Machado Filho
2017-06-02 14:04 ` Adhemerval Zanella
2017-05-04 12:51 ` [PATCH v2 1/2] manual: Add preadv and pwritev documentation Florian Weimer
2017-05-04 13:47 ` Adhemerval Zanella
2017-05-04 18:46 ` Adhemerval Zanella
2017-05-04 18:46 ` Florian Weimer
2017-05-04 18:53 ` Adhemerval Zanella
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