Move liblttng-ust to 'src/lib/'

[lttng-ust.git] / src / lib / lttng-ust / lttng-context-mnt-ns.c

diff --git a/src/lib/lttng-ust/lttng-context-mnt-ns.c b/src/lib/lttng-ust/lttng-context-mnt-ns.c
new file mode 100644 (file)
index 0000000..6181262
--- /dev/null
+++ b/src/lib/lttng-ust/lttng-context-mnt-ns.c
@@ -0,0 +1,131 @@
+/*
+ * SPDX-License-Identifier: LGPL-2.1-only
+ *
+ * Copyright (C) 2009-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ * Copyright (C) 2019 Michael Jeanson <mjeanson@efficios.com>
+ *
+ * LTTng UST mnt namespace context.
+ */
+
+#define _LGPL_SOURCE
+#include <limits.h>
+#include <stddef.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <lttng/ust-events.h>
+#include <lttng/ust-tracer.h>
+#include <lttng/ringbuffer-context.h>
+
+#include "context-internal.h"
+#include "ns.h"
+
+/*
+ * We cache the result to ensure we don't stat(2) the proc filesystem on
+ * each event. The mount namespace is global to the process.
+ */
+static ino_t cached_mnt_ns = NS_INO_UNINITIALIZED;
+
+static
+ino_t get_mnt_ns(void)
+{
+       struct stat sb;
+       ino_t mnt_ns;
+
+       mnt_ns = CMM_LOAD_SHARED(cached_mnt_ns);
+
+       /*
+        * If the cache is populated, do nothing and return the
+        * cached inode number.
+        */
+       if (caa_likely(mnt_ns != NS_INO_UNINITIALIZED))
+               return mnt_ns;
+
+       /*
+        * At this point we have to populate the cache, set the initial
+        * value to NS_INO_UNAVAILABLE (0), if we fail to get the inode
+        * number from the proc filesystem, this is the value we will
+        * cache.
+        */
+       mnt_ns = NS_INO_UNAVAILABLE;
+
+       if (stat("/proc/self/ns/mnt", &sb) == 0) {
+               mnt_ns = sb.st_ino;
+       }
+
+       /*
+        * And finally, store the inode number in the cache.
+        */
+       CMM_STORE_SHARED(cached_mnt_ns, mnt_ns);
+
+       return mnt_ns;
+}
+
+/*
+ * The mnt namespace can change for 3 reasons
+ *  * clone(2) called with CLONE_NEWNS
+ *  * setns(2) called with the fd of a different mnt ns
+ *  * unshare(2) called with CLONE_NEWNS
+ */
+void lttng_context_mnt_ns_reset(void)
+{
+       CMM_STORE_SHARED(cached_mnt_ns, NS_INO_UNINITIALIZED);
+}
+
+static
+size_t mnt_ns_get_size(void *priv __attribute__((unused)),
+               size_t offset)
+{
+       size_t size = 0;
+
+       size += lttng_ust_lib_ring_buffer_align(offset, lttng_ust_rb_alignof(ino_t));
+       size += sizeof(ino_t);
+       return size;
+}
+
+static
+void mnt_ns_record(void *priv __attribute__((unused)),
+                struct lttng_ust_lib_ring_buffer_ctx *ctx,
+                struct lttng_ust_channel_buffer *chan)
+{
+       ino_t mnt_ns;
+
+       mnt_ns = get_mnt_ns();
+       chan->ops->event_write(ctx, &mnt_ns, sizeof(mnt_ns), lttng_ust_rb_alignof(mnt_ns));
+}
+
+static
+void mnt_ns_get_value(void *priv __attribute__((unused)),
+               struct lttng_ust_ctx_value *value)
+{
+       value->u.s64 = get_mnt_ns();
+}
+
+static const struct lttng_ust_ctx_field *ctx_field = lttng_ust_static_ctx_field(
+       lttng_ust_static_event_field("mnt_ns",
+               lttng_ust_static_type_integer(sizeof(ino_t) * CHAR_BIT,
+                               lttng_ust_rb_alignof(ino_t) * CHAR_BIT,
+                               lttng_ust_is_signed_type(ino_t),
+                               BYTE_ORDER, 10),
+               false, false),
+       mnt_ns_get_size,
+       mnt_ns_record,
+       mnt_ns_get_value,
+       NULL, NULL);
+
+int lttng_add_mnt_ns_to_ctx(struct lttng_ust_ctx **ctx)
+{
+       int ret;
+
+       if (lttng_find_context(*ctx, ctx_field->event_field->name)) {
+               ret = -EEXIST;
+               goto error_find_context;
+       }
+       ret = lttng_ust_context_append(ctx, ctx_field);
+       if (ret)
+               return ret;
+       return 0;
+
+error_find_context:
+       return ret;
+}