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[Qemu-devel] [PATCH for 2.6] block: convert iscsi target to a valid ID f

From: Daniel P. Berrange
Subject: [Qemu-devel] [PATCH for 2.6] block: convert iscsi target to a valid ID for -iscsi arg lookup
Date: Wed, 13 Apr 2016 15:18:20 +0100

The iSCSI block driver has a very strange approach whereby it
does not accept options directly as part of the -drive arg,
but instead takes them indirectly from a -iscsi arg. To make
up -driver and -iscsi args, it takes the iSCSI target name
and uses that as an ID value for the -iscsi arg lookup.

For example, given a -drive arg that looks like


The iSCSI driver will try to find the -iscsi arg with an
id of "iqn.2013-12.com.example:iscsi-chap-netpool" eg it


Unfortunately this is impossible to actually do in practice
because almost all iSCSI target names contain a ':' which
is not a valid ID character for QEMU:

 $ qemu-system-x86_64: -iscsi 
Parameter 'id' expects an identifier
 Identifiers consist of letters, digits, '-', '.', '_', starting with a letter.

So for this to work we need to remove the invalid characters
in some manner. This patch takes the simplest possible approach
of just converting all invalid characters into underscores. eg
you can now use

 $ qemu-system-x86_64: -iscsi 
Parameter 'id' expects an identifier

There is theoretically the possibility for collison with this
approach if there were 2 iSCSI luns attached to the same VM
with target names that clash on the escaped char: eg


but in reality this will never happen. In addition in QEMU 2.7
the need to use the -iscsi arg will be removed by allowing all
the desired options to be listed directly with -drive. IOW this
quick stripping of invalid characters is just a short term fix
that will ultimately go away. For this reason it is not thought
worthwhile to invent a full collision-free escaping syntax for
iSCSI target IDs.

Signed-off-by: Daniel P. Berrange <address@hidden>

Note this problem was previously raised:


and discussed the following month:


 block/iscsi.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/block/iscsi.c b/block/iscsi.c
index 302baf8..7475cc9 100644
--- a/block/iscsi.c
+++ b/block/iscsi.c
@@ -1070,6 +1070,22 @@ retry:
     return 0;
+static char *convert_target_to_id(const char *target)
+    char *id = g_strdup(target);
+    size_t i;
+    for (i = 1; id[i]; i++) {
+        if (!qemu_isalnum(id[i]) && !strchr("-._", id[i])) {
+            id[i] = '_';
+        }
+    }
+    return id;
 static void parse_chap(struct iscsi_context *iscsi, const char *target,
                        Error **errp)
@@ -1079,13 +1095,16 @@ static void parse_chap(struct iscsi_context *iscsi, 
const char *target,
     const char *password = NULL;
     const char *secretid;
     char *secret = NULL;
+    char *targetid = NULL;
     list = qemu_find_opts("iscsi");
     if (!list) {
-    opts = qemu_opts_find(list, target);
+    targetid = convert_target_to_id(target);
+    opts = qemu_opts_find(list, targetid);
+    g_free(targetid);
     if (opts == NULL) {
         opts = QTAILQ_FIRST(&list->head);
         if (!opts) {

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