io: Add new qio_channel_read{, v}_all_eof functions

Some callers want to distinguish between clean EOF (no bytes read)
vs. a short read (at least one byte read, but EOF encountered
before reaching the desired length), as it allows clients the
ability to do a graceful shutdown when a server shuts down at
defined safe points in the protocol, rather than treating all
shutdown scenarios as an error due to EOF.  However, we don't want
to require all callers to have to check for early EOF.  So add
another wrapper function that can be used by the callers that care
about the distinction.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20170905191114.5959-3-eblake@redhat.com>
Acked-by: Daniel P. Berrange <berrange@redhat.com>

1 files changed, 40 insertions, 8 deletions

diff --git a/io/channel.c b/io/channel.c
index 9e62794cab..ec4b86de7c 100644
--- a/io/channel.c
+++ b/io/channel.c
@@ -86,16 +86,16 @@ ssize_t qio_channel_writev_full(QIOChannel *ioc,
 }
 
 
-
-int qio_channel_readv_all(QIOChannel *ioc,
-                          const struct iovec *iov,
-                          size_t niov,
-                          Error **errp)
+int qio_channel_readv_all_eof(QIOChannel *ioc,
+                              const struct iovec *iov,
+                              size_t niov,
+                              Error **errp)
 {
     int ret = -1;
     struct iovec *local_iov = g_new(struct iovec, niov);
     struct iovec *local_iov_head = local_iov;
     unsigned int nlocal_iov = niov;
+    bool partial = false;
 
     nlocal_iov = iov_copy(local_iov, nlocal_iov,
                           iov, niov,
@@ -114,21 +114,43 @@ int qio_channel_readv_all(QIOChannel *ioc,
         } else if (len < 0) {
             goto cleanup;
         } else if (len == 0) {
-            error_setg(errp,
-                       "Unexpected end-of-file before all bytes were read");
+            if (partial) {
+                error_setg(errp,
+                           "Unexpected end-of-file before all bytes were read");
+            } else {
+                ret = 0;
+            }
             goto cleanup;
         }
 
+        partial = true;
         iov_discard_front(&local_iov, &nlocal_iov, len);
     }
 
-    ret = 0;
+    ret = 1;
 
  cleanup:
     g_free(local_iov_head);
     return ret;
 }
 
+int qio_channel_readv_all(QIOChannel *ioc,
+                          const struct iovec *iov,
+                          size_t niov,
+                          Error **errp)
+{
+    int ret = qio_channel_readv_all_eof(ioc, iov, niov, errp);
+
+    if (ret == 0) {
+        ret = -1;
+        error_setg(errp,
+                   "Unexpected end-of-file before all bytes were read");
+    } else if (ret == 1) {
+        ret = 0;
+    }
+    return ret;
+}
+
 int qio_channel_writev_all(QIOChannel *ioc,
                            const struct iovec *iov,
                            size_t niov,
@@ -205,6 +227,16 @@ ssize_t qio_channel_write(QIOChannel *ioc,
 }
 
 
+int qio_channel_read_all_eof(QIOChannel *ioc,
+                             char *buf,
+                             size_t buflen,
+                             Error **errp)
+{
+    struct iovec iov = { .iov_base = buf, .iov_len = buflen };
+    return qio_channel_readv_all_eof(ioc, &iov, 1, errp);
+}
+
+
 int qio_channel_read_all(QIOChannel *ioc,
                          char *buf,
                          size_t buflen,