[Qemu-devel] [PATCH] Force pread64/pwrite64 to return 0 for zero-length buffer

[Ilya Palachev]

According to official standard POSIX.1-2001. pread64 and pwrite64
should return 0 for zero-length buffers as mentioned at

http://pubs.opengroup.org/onlinepubs/009695399/functions/read.html
http://pubs.opengroup.org/onlinepubs/009695399/functions/write.html

Change-Id: Icd66ea29658329fbd5e6461d1def0c78c81d2671
Signed-off-by: Ilya Palachev <address@hidden>
---
 linux-user/syscall.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index a41dd43..a08f5ef 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -8127,6 +8127,10 @@ abi_long do_syscall(void *cpu_env, int num, abi_ulong 
arg1,
             arg4 = arg5;
             arg5 = arg6;
         }
+        if (!arg3) {
+            ret = 0;
+            break;
+        }
         if (!(p = lock_user(VERIFY_WRITE, arg2, arg3, 0)))
             goto efault;
         ret = get_errno(pread64(arg1, p, arg3, target_offset64(arg4, arg5)));
@@ -8137,6 +8141,10 @@ abi_long do_syscall(void *cpu_env, int num, abi_ulong 
arg1,
             arg4 = arg5;
             arg5 = arg6;
         }
+        if (!arg3) {
+            ret = 0;
+            break;
+        }
         if (!(p = lock_user(VERIFY_READ, arg2, arg3, 1)))
             goto efault;
         ret = get_errno(pwrite64(arg1, p, arg3, target_offset64(arg4, arg5)));
-- 
2.1.3