Tools: hv: update buffer handling in hv_fcopy_daemon

Currently this warning is triggered when compiling hv_fcopy_daemon:

hv_fcopy_daemon.c:216:4: warning: dereferencing type-punned pointer will break
strict-aliasing rules [-Wstrict-aliasing]
    kernel_modver = *(__u32 *)buffer;

Convert the send/receive buffer to a union and pass individual members as
needed. This also gives the correct size for the buffer.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 17 insertions, 15 deletions

diff --git a/tools/hv/hv_fcopy_daemon.c b/tools/hv/hv_fcopy_daemon.c
index 26ae609a9448..457a1521f32f 100644
--- a/tools/hv/hv_fcopy_daemon.c
+++ b/tools/hv/hv_fcopy_daemon.c
@@ -138,14 +138,17 @@ void print_usage(char *argv[])
 
 int main(int argc, char *argv[])
 {
-        int fcopy_fd, len;
+        int fcopy_fd;
         int error;
         int daemonize = 1, long_index = 0, opt;
         int version = FCOPY_CURRENT_VERSION;
-        char *buffer[4096 * 2];
-        struct hv_fcopy_hdr *in_msg;
+        union {
+                struct hv_fcopy_hdr hdr;
+                struct hv_start_fcopy start;
+                struct hv_do_fcopy copy;
+                __u32 kernel_modver;
+        } buffer = { };
         int in_handshake = 1;
-        __u32 kernel_modver;
 
         static struct option long_options[] = {
                 {"help",        no_argument,       0,  'h' },
@@ -195,32 +198,31 @@ int main(int argc, char *argv[])
                  * In this loop we process fcopy messages after the
                  * handshake is complete.
                  */
-                len = pread(fcopy_fd, buffer, (4096 * 2), 0);
+                ssize_t len;
+
+                len = pread(fcopy_fd, &buffer, sizeof(buffer), 0);
                 if (len < 0) {
                         syslog(LOG_ERR, "pread failed: %s", strerror(errno));
                         exit(EXIT_FAILURE);
                 }
 
                 if (in_handshake) {
-                        if (len != sizeof(kernel_modver)) {
+                        if (len != sizeof(buffer.kernel_modver)) {
                                 syslog(LOG_ERR, "invalid version negotiation");
                                 exit(EXIT_FAILURE);
                         }
-                        kernel_modver = *(__u32 *)buffer;
                         in_handshake = 0;
-                        syslog(LOG_INFO, "kernel module version: %d",
-                               kernel_modver);
+                        syslog(LOG_INFO, "kernel module version: %u",
+                               buffer.kernel_modver);
                         continue;
                 }
 
-                in_msg = (struct hv_fcopy_hdr *)buffer;
-
-                switch (in_msg->operation) {
+                switch (buffer.hdr.operation) {
                 case START_FILE_COPY:
-                        error = hv_start_fcopy((struct hv_start_fcopy *)in_msg);
+                        error = hv_start_fcopy(&buffer.start);
                         break;
                 case WRITE_TO_FILE:
-                        error = hv_copy_data((struct hv_do_fcopy *)in_msg);
+                        error = hv_copy_data(&buffer.copy);
                         break;
                 case COMPLETE_FCOPY:
                         error = hv_copy_finished();
@@ -231,7 +233,7 @@ int main(int argc, char *argv[])
 
                 default:
                         syslog(LOG_ERR, "Unknown operation: %d",
-                                in_msg->operation);
+                                buffer.hdr.operation);
 
                 }