[PATCH v2 4/5] dump: Improve some dump-guest-memory error messages

[Markus Armbruster <armbru@redhat.com>]

Zero @length is rejected with "Invalid parameter 'length'".  Improve
to "parameter 'length' expects a non-zero length".

qemu_open_old() is a wrapper around qemu_open_internal() that throws
away error information.  Switch to the wrapper that doesn't:
qemu_create().  Example improvement:

    (qemu) dump-guest-memory /dev/fdset/x 0 1
    Error: Could not open '/dev/fdset/x': Invalid argument

becomes

    Error: Could not parse fdset /dev/fdset/x

@protocol values not starting with "fd:" or "file:" are rejected with
"Invalid parameter 'protocol'".  Improve to "parameter 'protocol' must
start with 'file:' or 'fd:'".

While there, make the conditional checking @protocol a little more
obvious.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 dump/dump.c | 18 +++++++-----------
 1 file changed, 7 insertions(+), 11 deletions(-)

diff --git a/dump/dump.c b/dump/dump.c
index 30fb2cb0c6..66f62d0891 100644
--- a/dump/dump.c
+++ b/dump/dump.c
@@ -1810,7 +1810,7 @@ static void dump_init(DumpState *s, int fd, bool has_format,
 
     s->fd = fd;
     if (has_filter && !length) {
-        error_setg(errp, QERR_INVALID_PARAMETER, "length");
+        error_setg(errp, "parameter 'length' expects a non-zero size");
         goto cleanup;
     }
     s->filter_area_begin = begin;
@@ -2070,7 +2070,7 @@ void qmp_dump_guest_memory(bool paging, const char *protocol,
 {
     ERRP_GUARD();
     const char *p;
-    int fd = -1;
+    int fd;
     DumpState *s;
     bool detach_p = false;
 
@@ -2133,18 +2133,14 @@ void qmp_dump_guest_memory(bool paging, const char *protocol,
         if (fd == -1) {
             return;
         }
-    }
-
-    if  (strstart(protocol, "file:", &p)) {
-        fd = qemu_open_old(p, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY, S_IRUSR);
+    } else if  (strstart(protocol, "file:", &p)) {
+        fd = qemu_create(p, O_WRONLY | O_TRUNC | O_BINARY, S_IRUSR, errp);
         if (fd < 0) {
-            error_setg_file_open(errp, errno, p);
             return;
         }
-    }
-
-    if (fd == -1) {
-        error_setg(errp, QERR_INVALID_PARAMETER, "protocol");
+    } else {
+        error_setg(errp,
+                   "parameter 'protocol' must start with 'file:' or 'fd:'");
         return;
     }
 
-- 
2.41.0