Hi,
RFC:
Sometimes, when there are multiple processes generating time-based
UUIDs in a loop (each of them using multiple threads), it can happen
that the socket backlog in uuidd daemon is full and so the connection
request is refused. uuid_generate_time() then fallbacks to unsafe way of
generating UUID, which may cause duplicate time-based UUIDs to be
generated.
The problem with libuuid interface is that it is impossible to
inform the caller of uuid_generate_time() that unsafe fallback has
been used (the function returns void).
This patch introduces new function,
int uuid_generate_time_nf(uuid_t out) /* nf = "no fallback" */
which, in case uuidd was needed, but for whatever reason could not be
used, returns -1 and leaves content in @out undefined.
Signed-off-by: Petr Uzel <petr.uzel@xxxxxxx>
---
shlibs/uuid/src/gen_uuid.c | 40 +++++++++++++++++++++++++++++++++++-----
shlibs/uuid/src/uuid.h | 1 +
shlibs/uuid/src/uuid.sym | 10 +++++++++-
3 files changed, 45 insertions(+), 6 deletions(-)
diff --git a/shlibs/uuid/src/gen_uuid.c b/shlibs/uuid/src/gen_uuid.c
index a90bd8e..45af07f 100644
--- a/shlibs/uuid/src/gen_uuid.c
+++ b/shlibs/uuid/src/gen_uuid.c
@@ -587,7 +587,17 @@ void uuid__generate_time(uuid_t out, int *num)
uuid_pack(&uu, out);
}
-void uuid_generate_time(uuid_t out)
+/*
+ * Generate time-based UUID and store it to @out
+ *
+ * If @fallback is nonzero and uuidd is needed, but could not be used,
+ * then do not use the usafe fallback.
+ *
+ * Returns 0 on success, -1 on failure (could not connect to uuidd and
+ * @fallback=0)
+ *
+ */
+static int uuid_generate_time_generic(uuid_t out, int fallback)
{
#ifdef HAVE_TLS
THREAD_LOCAL int num = 0;
@@ -607,7 +617,7 @@ void uuid_generate_time(uuid_t out)
last_time = time(0);
uuid_unpack(out, &uu);
num--;
- return;
+ return 0;
}
num = 0;
}
@@ -620,14 +630,34 @@ void uuid_generate_time(uuid_t out)
}
num--;
uuid_pack(&uu, out);
- return;
+ return 0;
}
#else
if (get_uuid_via_daemon(UUIDD_OP_TIME_UUID, out, 0) == 0)
- return;
+ return 0;
#endif
- uuid__generate_time(out, 0);
+ if (fallback) {
+ uuid__generate_time(out, 0);
+ return 0;
+ }
+ else
+ /* fallback==0: disabled */
+ return -1;
+}
+
+void uuid_generate_time(uuid_t out)
+{
+ (void)uuid_generate_time_generic(out, 1);
+}
+
+
+/*
+ * Same as uuid_generate_time, but with unsafe fallback disabled.
+ */
+int uuid_generate_time_nf(uuid_t out)
+{
+ return uuid_generate_time_generic(out, 0);
}
diff --git a/shlibs/uuid/src/uuid.h b/shlibs/uuid/src/uuid.h
index e329bf7..c7442ee 100644
--- a/shlibs/uuid/src/uuid.h
+++ b/shlibs/uuid/src/uuid.h
@@ -79,6 +79,7 @@ void uuid_copy(uuid_t dst, const uuid_t src);
void uuid_generate(uuid_t out);
void uuid_generate_random(uuid_t out);
void uuid_generate_time(uuid_t out);
+int uuid_generate_time_nf(uuid_t out);
/* isnull.c */
int uuid_is_null(const uuid_t uu);
diff --git a/shlibs/uuid/src/uuid.sym b/shlibs/uuid/src/uuid.sym
index 05d9f39..719f133 100644
--- a/shlibs/uuid/src/uuid.sym
+++ b/shlibs/uuid/src/uuid.sym
@@ -1,6 +1,6 @@
/*
* The symbol versioning ensures that a new application requiring symbol foo()
- * can't run with old libblkid.so not providing foo() - the global SONAME
+ * can't run with old libuuid.so not providing foo() - the global SONAME
* version info can't enforce this since we never change the SONAME.
*
* The original libuuid from e2fsprogs (<=1.41.5) does not to use
@@ -31,3 +31,11 @@ global:
local:
*;
};
+
+/*
+ * version(s) since util-linux 2.19
+ */
+UUID_2.19 {
+global:
+ uuid_generate_time_nf;
+} UUID_1.0;
--
1.7.1
Petr
--
Petr Uzel
IRC: ptr_uzl @ freenode
Attachment:
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