[Qemu-devel] [PULL 23/24] linux-user: writev Partial Writes

[riku . voipio]

From: Tom Musta <address@hidden>

Although not technically not required by POSIX, the writev system call will
typically write out its buffers individually.  That is, if the first buffer
is written successfully, but the second buffer pointer is invalid, then
the first chuck will be written and its size is returned.

Signed-off-by: Tom Musta <address@hidden>
Reviewed-by: Peter Maydell <address@hidden>
Signed-off-by: Riku Voipio <address@hidden>
---
 linux-user/syscall.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index c4f6454..3b1beff 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -1803,6 +1803,7 @@ static struct iovec *lock_iovec(int type, abi_ulong 
target_addr,
     abi_ulong total_len, max_len;
     int i;
     int err = 0;
+    bool bad_address = false;
 
     if (count == 0) {
         errno = 0;
@@ -1843,9 +1844,20 @@ static struct iovec *lock_iovec(int type, abi_ulong 
target_addr,
             vec[i].iov_base = 0;
         } else {
             vec[i].iov_base = lock_user(type, base, len, copy);
+            /* If the first buffer pointer is bad, this is a fault.  But
+             * subsequent bad buffers will result in a partial write; this
+             * is realized by filling the vector with null pointers and
+             * zero lengths. */
             if (!vec[i].iov_base) {
-                err = EFAULT;
-                goto fail;
+                if (i == 0) {
+                    err = EFAULT;
+                    goto fail;
+                } else {
+                    bad_address = true;
+                }
+            }
+            if (bad_address) {
+                len = 0;
             }
             if (len > max_len - total_len) {
                 len = max_len - total_len;
-- 
2.0.1