[Xen-changelog] [qemu-xen master] nbd: Don't inf-loop on early EOF

[patchbot@xxxxxxx]

commit a5068244b4f0c994791303b6186b6f732adab6c2
Author:     Eric Blake <eblake@xxxxxxxxxx>
AuthorDate: Mon Nov 7 14:38:13 2016 -0600
Commit:     Paolo Bonzini <pbonzini@xxxxxxxxxx>
CommitDate: Thu Nov 10 16:01:30 2016 +0100

    nbd: Don't inf-loop on early EOF
    
    Commit 7d3123e converted a single read_sync() into a while loop
    that assumed that read_sync() would either make progress or give
    an error. But when the server hangs up early, the client sees
    EOF (a read_sync() of 0) and never makes progress, which in turn
    caused qemu-iotest './check -nbd 83' to go into an infinite loop.
    
    Rework the loop to accomodate reads cut short by EOF.
    
    Reported-by: Max Reitz <mreitz@xxxxxxxxxx>
    Signed-off-by: Eric Blake <eblake@xxxxxxxxxx>
    Message-Id: <1478551093-32757-1-git-send-email-eblake@xxxxxxxxxx>
    Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
 nbd/client.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/nbd/client.c b/nbd/client.c
index 7db4301..ffb0743 100644
--- a/nbd/client.c
+++ b/nbd/client.c
@@ -90,20 +90,21 @@ static QTAILQ_HEAD(, NBDExport) exports = 
QTAILQ_HEAD_INITIALIZER(exports);
  * the amount of bytes consumed. */
 static ssize_t drop_sync(QIOChannel *ioc, size_t size)
 {
-    ssize_t ret, dropped = size;
+    ssize_t ret = 0;
     char small[1024];
     char *buffer;
 
     buffer = sizeof(small) < size ? small : g_malloc(MIN(65536, size));
     while (size > 0) {
-        ret = read_sync(ioc, buffer, MIN(65536, size));
-        if (ret < 0) {
+        ssize_t count = read_sync(ioc, buffer, MIN(65536, size));
+
+        if (count <= 0) {
             goto cleanup;
         }
-        assert(ret <= size);
-        size -= ret;
+        assert(count <= size);
+        size -= count;
+        ret += count;
     }
-    ret = dropped;
 
  cleanup:
     if (buffer != small) {
--
generated by git-patchbot for /home/xen/git/qemu-xen.git#master

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