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[Qemu-devel] [PATCH 79/97] linux-user: write(fd, NULL, 0) parity with li
From: |
Michael Roth |
Subject: |
[Qemu-devel] [PATCH 79/97] linux-user: write(fd, NULL, 0) parity with linux's treatment of same |
Date: |
Mon, 1 Apr 2019 15:59:53 -0500 |
From: Tony Garnock-Jones <address@hidden>
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>
Reviewed-by: Philippe Mathieu-Daudé <address@hidden>
Reviewed-by: Laurent Vivier <address@hidden>
Message-Id: <address@hidden>
Signed-off-by: Laurent Vivier <address@hidden>
(cherry picked from commit 58cfa6c2e6eb51b23cc98f81d16136b3ca929b31)
Signed-off-by: Michael Roth <address@hidden>
---
linux-user/syscall.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 5a4af76c03..1477509cf2 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -8077,6 +8077,9 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
}
break;
case TARGET_NR_write:
+ if (arg2 == 0 && arg3 == 0) {
+ return get_errno(safe_write(arg1, 0, 0));
+ }
if (!(p = lock_user(VERIFY_READ, arg2, arg3, 1)))
goto efault;
if (fd_trans_target_to_host_data(arg1)) {
--
2.17.1
- Re: [Qemu-devel] [PATCH 59/97] target/xtensa: drop num_[core_]regs from dc232b/dc233c configs, (continued)
- [Qemu-devel] [PATCH 32/97] vhost: fix invalid downcast, Michael Roth, 2019/04/01
- [Qemu-devel] [PATCH 69/97] nbd/server: Advertise all contexts in response to bare LIST, Michael Roth, 2019/04/01
- [Qemu-devel] [PATCH 71/97] nbd/client: Send NBD_CMD_DISC if open fails after connect, Michael Roth, 2019/04/01
- [Qemu-devel] [PATCH 76/97] pcie: set link state inactive/active after hot unplug/plug, Michael Roth, 2019/04/01
- [Qemu-devel] [PATCH 75/97] Changes requirement for "vsubsbs" instruction, Michael Roth, 2019/04/01
- [Qemu-devel] [PATCH 22/97] aio: Do aio_notify_accept only during blocking aio_poll, Michael Roth, 2019/04/01
- [Qemu-devel] [PATCH 44/97] target/arm: Fix cpu_get_tb_cpu_state() for non-SVE CPUs, Michael Roth, 2019/04/01
- [Qemu-devel] [PATCH 93/97] qga: update docs with systemd suspend support info, Michael Roth, 2019/04/01
- [Qemu-devel] [PATCH 74/97] iotests: make 235 work on s390 (and others), Michael Roth, 2019/04/01
- [Qemu-devel] [PATCH 79/97] linux-user: write(fd, NULL, 0) parity with linux's treatment of same,
Michael Roth <=
- [Qemu-devel] [PATCH 29/97] target/xtensa: fix FPU2000 bugs, Michael Roth, 2019/04/01
- [Qemu-devel] [PATCH 64/97] qemu-img: Fix leak, Michael Roth, 2019/04/01
- [Qemu-devel] [PATCH 81/97] s390x: Return specification exception for unimplemented diag 308 subcodes, Michael Roth, 2019/04/01
- [Qemu-devel] [PATCH 02/97] target/arm: Fix typo in do_sat_addsub_64, Michael Roth, 2019/04/01
- [Qemu-devel] [PATCH 86/97] tpm: Make sure the locality received from backend is valid, Michael Roth, 2019/04/01
- [Qemu-devel] [PATCH 01/97] target/arm: Fix sign of sve_cmpeq_ppzw/sve_cmpne_ppzw, Michael Roth, 2019/04/01
- [Qemu-devel] [PATCH 63/97] qemu-img: Fix typo, Michael Roth, 2019/04/01
- [Qemu-devel] [PATCH 41/97] block/rbd: Attempt to parse legacy filenames, Michael Roth, 2019/04/01
- [Qemu-devel] [PATCH 80/97] linux-user: make pwrite64/pread64(fd, NULL, 0, offset) return 0, Michael Roth, 2019/04/01
- [Qemu-devel] [PATCH 58/97] vhost-scsi: prevent using uninitialized vqs, Michael Roth, 2019/04/01