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Re: [Qemu-stable] [Qemu-devel] [PATCH] linux-user: write(fd, NULL, 0) pa
From: |
Laurent Vivier |
Subject: |
Re: [Qemu-stable] [Qemu-devel] [PATCH] linux-user: write(fd, NULL, 0) parity with linux's treatment of same |
Date: |
Sun, 9 Sep 2018 10:22:23 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 |
Le 08/09/2018 à 20:22, Tony Garnock-Jones a écrit :
> Bring linux-user write(2) handling into line with linux for the case
> of a 0-byte write with a NULL buffer. Based on a patch originally
> written by Zhuowei Zhang.
>
> Addresses https://bugs.launchpad.net/qemu/+bug/1716292.
>
> From Zhuowei Zhang's patch
> (https://lists.gnu.org/archive/html/qemu-devel/2017-09/msg08073.html):
>
> Linux returns success for the special case of calling write with a
> zero-length NULL buffer: compiling and running
>
> int main() {
> ssize_t ret = write(STDOUT_FILENO, NULL, 0);
> fprintf(stderr, "write returned %ld\n", ret);
> return 0;
> }
>
> gives "write returned 0" when run directly, but "write returned
> -1" in QEMU.
>
> This commit checks for this situation and returns success if
> found.
>
> Subsequent discussion raised the following questions (and my answers):
>
> - Q. Should TARGET_NR_read pass through to safe_read in this
> situation too?
> A. I'm wary of changing unrelated code to the specific problem I'm
> addressing. TARGET_NR_read is already consistent with Linux for
> this case.
>
> - Q. Do pread64/pwrite64 need to be changed similarly?
> A. Experiment suggests not: both linux and linux-user yield -1 for
> NULL 0-length reads/writes.
>
> Signed-off-by: Tony Garnock-Jones <address@hidden>
> ---
> linux-user/syscall.c | 3 +++
> 1 file changed, 3 insertions(+)
Reviewed-by: Laurent Vivier <address@hidden>