[Xen-devel] [PATCH 3/3] qemu-xen: fixes to support the console based save/restore

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

The PV console backend for stubdoms is qemu-xen in dom0; we need to make
sure it is able to support read/write to a file as console input/output.
Unfortunately the current file: "char device" only opens the file O_WRONLY,
so this patch adds a new "char device" called filerw: that opens the
file O_RDWR.

We need to issue reads with the exact number of bytes to read the
qemu-xen save file, and to do that this patch disables buffering on all
the savevm reads/writes for stubdoms.

Finally this patch fixes a bug in the xen_console disconnect handler
that causes qemu-xen to segfaults.

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>


diff --git a/hw/xen_console.c b/hw/xen_console.c
index d7099c4..0a2374c 100644
--- a/hw/xen_console.c
+++ b/hw/xen_console.c
@@ -258,7 +258,7 @@ static void con_disconnect(struct XenDevice *xendev)
     xen_be_unbind_evtchn(&con->xendev);
 
     if (con->sring) {
-        if (!xendev->gnttabdev)
+        if (!xendev->dev)
            munmap(con->sring, XC_PAGE_SIZE);
         else
             xc_gnttab_munmap(xendev->gnttabdev, con->sring, 1);
diff --git a/qemu-char.c b/qemu-char.c
index 7a6a33d..22acfe6 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -594,6 +594,16 @@ static CharDriverState *qemu_chr_open_file_out(const char 
*file_out)
     return qemu_chr_open_fd(-1, fd_out);
 }
 
+static CharDriverState *qemu_chr_open_file_rw(const char *file_rw)
+{
+    int fd_rw;
+
+    TFR(fd_rw = open(file_rw, O_RDWR | O_CREAT | O_BINARY, 0666));
+    if (fd_rw < 0)
+        return NULL;
+    return qemu_chr_open_fd(fd_rw, fd_rw);
+}
+
 static CharDriverState *qemu_chr_open_pipe(const char *filename)
 {
     int fd_in, fd_out;
@@ -2164,6 +2174,8 @@ CharDriverState *qemu_chr_open(const char *label, const 
char *filename, void (*i
        chr = qemu_chr_open_tcp(p, 0, 1);
     } else if (strstart(filename, "file:", &p)) {
         chr = qemu_chr_open_file_out(p);
+    } else if (strstart(filename, "filerw:", &p)) {
+        chr = qemu_chr_open_file_rw(p);
     } else if (strstart(filename, "pipe:", &p)) {
         chr = qemu_chr_open_pipe(p);
     } else if (!strcmp(filename, "pty")) {
diff --git a/savevm.c b/savevm.c
index b66f7e2..71a57eb 100644
--- a/savevm.c
+++ b/savevm.c
@@ -133,7 +133,13 @@ void qemu_announce_self(void)
 /***********************************************************/
 /* savevm/loadvm support */
 
+#ifdef CONFIG_STUBDOM
+/* disable buffering for stubdoms because we need to issue reads for the
+ * exact number of bytes */
+#define IO_BUF_SIZE 1
+#else
 #define IO_BUF_SIZE 32768
+#endif
 
 struct QEMUFile {
     QEMUFilePutBufferFunc *put_buffer;
@@ -303,6 +309,10 @@ QEMUFile *qemu_fopen(const char *filename, const char 
*mode)
     if (!s->outfile)
         goto fail;
 
+#ifdef CONFIG_STUBDOM
+    setvbuf(s->outfile, NULL, _IONBF, 0);
+#endif
+
     if (!strcmp(mode, "wb"))
         return qemu_fopen_ops(s, file_put_buffer, NULL, file_close, NULL);
     else if (!strcmp(mode, "rb"))

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