Re: [Qemu-devel] [PATCH] linux-user: make pwrite64/pread64(fd, NULL, 0, offset) return 0

[Laurent Vivier <laurent@vivier.eu>]

Le 08/01/2019 à 19:49, Peter Maydell a écrit :
> Linux returns success if pwrite64() or pread64() are called with a
> zero length NULL buffer, but QEMU was returning -TARGET_EFAULT.
> 
> This is the same bug that we fixed in commit 58cfa6c2e6eb51b23cc9
> for the write syscall, and long before that in 38d840e6790c29f59
> for the read syscall.
> 
> Fixes: https://bugs.launchpad.net/qemu/+bug/1810433
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> I chose to fix this by setting p to NULL and falling through
> to the normal-case codepath rather than having a call to
> pread/pwrite in the special-case if like 58cfa6c2e6eb5,
> because here the normal-case is a bit more complicated as
> it has the target_offset64() call in it.
> 38d840e6790c29f59 has "just return 0" for the NULL buffer
> case, but we can't do that here as that would not get the
> "negative offset should return -EINVAL" case write.
> ---
>  linux-user/syscall.c | 22 ++++++++++++++++++----
>  1 file changed, 18 insertions(+), 4 deletions(-)
> 

Reviewed-by: Laurent Vivier <laurent@vivier.eu>