ccid-card-passthru, dev-smartcard-reader: add debug environment variables

Introduces a new utility function: parse_debug_env to avoid code
duplication.

This overrides whatever debug value is set on the corresponding devices
from the command line, and is meant to ease the usage with any
management stack. For libvirt you can set environment variables by
extending the dom namespace, i.e:

<domain type='kvm' id='3' xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'>
  <qemu:commandline>
    <qemu:env name='QEMU_CCID_PASSTHRU_DEBUG' value='4'/>
    <qemu:env name='QEMU_CCID_DEBUG' value='4'/>
  </qemu:commandline>
</domain>
Signed-off-by: NAlon Levy <alevy@redhat.com>
Reviewed-by: NMarc-André Lureau <mlureau@redhat.com>

hw/usb/ccid-card-passthru.c

@@ -350,6 +350,8 @@ static int passthru_initfn(CCIDCardState *base)
         error_report("missing chardev");
         return -1;
     }
+    card->debug = parse_debug_env("QEMU_CCID_PASSTHRU_DEBUG", D_VERBOSE,
+                                  card->debug);
     assert(sizeof(DEFAULT_ATR) <= MAX_ATR_SIZE);
     memcpy(card->atr, DEFAULT_ATR, sizeof(DEFAULT_ATR));
     card->atr_length = sizeof(DEFAULT_ATR);

hw/usb/dev-smartcard-reader.c

@@ -1260,6 +1260,7 @@ static int ccid_initfn(USBDevice *dev)
     s->bulk_out_pos = 0;
     ccid_reset_parameters(s);
     ccid_reset(s);
+    s->debug = parse_debug_env("QEMU_CCID_DEBUG", D_VERBOSE, s->debug);
     return 0;
 }
 

include/qemu-common.h

@@ -482,4 +482,9 @@ can_use_buffer_find_nonzero_offset(const void *buf, size_t len)
 }
 size_t buffer_find_nonzero_offset(const void *buf, size_t len);
 
+/*
+ * helper to parse debug environment variables
+ */
+int parse_debug_env(const char *name, int max, int initial);
+
 #endif

util/cutils.c

@@ -482,3 +482,26 @@ int uleb128_decode_small(const uint8_t *in, uint32_t *n)
         return 2;
     }
 }
+
+/*
+ * helper to parse debug environment variables
+ */
+int parse_debug_env(const char *name, int max, int initial)
+{
+    char *debug_env = getenv(name);
+    char *inv = NULL;
+    int debug;
+
+    if (!debug_env) {
+        return initial;
+    }
+    debug = strtol(debug_env, &inv, 10);
+    if (inv == debug_env) {
+        return initial;
+    }
+    if (debug < 0 || debug > max) {
+        fprintf(stderr, "warning: %s not in [0, %d]", name, max);
+        return initial;
+    }
+    return debug;
+}