qemu-char: Print strerror message on failure

The only way for chardev drivers to communicate an error was to return a NULL
pointer, which resulted in an error message that said _that_ something went
wrong, but not _why_.

This patch changes the interface to return 0/-errno and updates
qemu_chr_open_opts to use strerror to display a more helpful error message.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

1 files changed, 5 insertions, 4 deletions

diff --git a/spice-qemu-char.c b/spice-qemu-char.c
index 605c24123..95bf6b65d 100644
--- a/spice-qemu-char.c
+++ b/spice-qemu-char.c
@@ -159,7 +159,7 @@ static void print_allowed_subtypes(void)
     fprintf(stderr, "\n");
 }
 
-CharDriverState *qemu_chr_open_spice(QemuOpts *opts)
+int qemu_chr_open_spice(QemuOpts *opts, CharDriverState **_chr)
 {
     CharDriverState *chr;
     SpiceCharDriver *s;
@@ -171,7 +171,7 @@ CharDriverState *qemu_chr_open_spice(QemuOpts *opts)
     if (name == NULL) {
         fprintf(stderr, "spice-qemu-char: missing name parameter\n");
         print_allowed_subtypes();
-        return NULL;
+        return -EINVAL;
     }
     for(;*psubtype != NULL; ++psubtype) {
         if (strcmp(name, *psubtype) == 0) {
@@ -182,7 +182,7 @@ CharDriverState *qemu_chr_open_spice(QemuOpts *opts)
     if (subtype == NULL) {
         fprintf(stderr, "spice-qemu-char: unsupported name\n");
         print_allowed_subtypes();
-        return NULL;
+        return -EINVAL;
     }
 
     chr = qemu_mallocz(sizeof(CharDriverState));
@@ -199,5 +199,6 @@ CharDriverState *qemu_chr_open_spice(QemuOpts *opts)
 
     qemu_chr_generic_open(chr);
 
-    return chr;
+    *_chr = chr;
+    return 0;
 }