[PATCH v2 4/4] net/mlx: make rdma-core glue path configurable

[Adrien Mazarguil <adrien.mazarguil@6wind.com>]

Since rdma-core glue libraries are intrinsically tied to their respective
PMDs and used as internal plug-ins, their presence in the default search
path among other system libraries for the dynamic linker is not necessarily
desired.

This commit enables their installation and subsequent look-up at run time
in RTE_EAL_PMD_PATH if configured to a nonempty string. This path can also
be overridden by environment variables MLX[45]_GLUE_PATH.

Signed-off-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>
---
 doc/guides/nics/mlx4.rst | 17 +++++++++++++++++
 doc/guides/nics/mlx5.rst | 14 ++++++++++++++
 drivers/net/mlx4/mlx4.c  | 43 ++++++++++++++++++++++++++++++++++++++++++-
 drivers/net/mlx5/mlx5.c  | 43 ++++++++++++++++++++++++++++++++++++++++++-
 4 files changed, 115 insertions(+), 2 deletions(-)

diff --git a/doc/guides/nics/mlx4.rst b/doc/guides/nics/mlx4.rst
index 88161781c..9e4fbf692 100644
--- a/doc/guides/nics/mlx4.rst
+++ b/doc/guides/nics/mlx4.rst
@@ -97,6 +97,11 @@ These options can be modified in the ``.config`` file.
   ``CONFIG_RTE_BUILD_SHARED_LIB`` disabled) and they won't show up as
   missing with ``ldd(1)``.
 
+  It works by moving these dependencies to a purpose-built rdma-core "glue"
+  plug-in, which must either be installed in ``CONFIG_RTE_EAL_PMD_PATH`` if
+  set, or in a standard location for the dynamic linker (e.g. ``/lib``) if
+  left to the default empty string (``""``).
+
   This option has no performance impact.
 
 - ``CONFIG_RTE_LIBRTE_MLX4_DEBUG`` (default **n**)
@@ -113,6 +118,18 @@ These options can be modified in the ``.config`` file.
 
   This value is always 1 for RX queues since they use a single MP.
 
+Environment variables
+~~~~~~~~~~~~~~~~~~~~~
+
+- ``MLX4_GLUE_PATH``
+
+  A list of directories in which to search for the rdma-core "glue" plug-in,
+  separated by colons or semi-colons.
+
+  Only matters when compiled with ``CONFIG_RTE_LIBRTE_MLX4_DLOPEN_DEPS``
+  enabled and most useful when ``CONFIG_RTE_EAL_PMD_PATH`` is also set,
+  since ``LD_LIBRARY_PATH`` has no effect in this case.
+
 Run-time configuration
 ~~~~~~~~~~~~~~~~~~~~~~
 
diff --git a/doc/guides/nics/mlx5.rst b/doc/guides/nics/mlx5.rst
index a9e4bf51a..1635dff2b 100644
--- a/doc/guides/nics/mlx5.rst
+++ b/doc/guides/nics/mlx5.rst
@@ -170,6 +170,11 @@ These options can be modified in the ``.config`` file.
   ``CONFIG_RTE_BUILD_SHARED_LIB`` disabled) and they won't show up as
   missing with ``ldd(1)``.
 
+  It works by moving these dependencies to a purpose-built rdma-core "glue"
+  plug-in, which must either be installed in ``CONFIG_RTE_EAL_PMD_PATH`` if
+  set, or in a standard location for the dynamic linker (e.g. ``/lib``) if
+  left to the default empty string (``""``).
+
   This option has no performance impact.
 
 - ``CONFIG_RTE_LIBRTE_MLX5_DEBUG`` (default **n**)
@@ -189,6 +194,15 @@ These options can be modified in the ``.config`` file.
 Environment variables
 ~~~~~~~~~~~~~~~~~~~~~
 
+- ``MLX5_GLUE_PATH``
+
+  A list of directories in which to search for the rdma-core "glue" plug-in,
+  separated by colons or semi-colons.
+
+  Only matters when compiled with ``CONFIG_RTE_LIBRTE_MLX5_DLOPEN_DEPS``
+  enabled and most useful when ``CONFIG_RTE_EAL_PMD_PATH`` is also set,
+  since ``LD_LIBRARY_PATH`` has no effect in this case.
+
 - ``MLX5_PMD_ENABLE_PADDING``
 
   Enables HW packet padding in PCI bus transactions.
diff --git a/drivers/net/mlx4/mlx4.c b/drivers/net/mlx4/mlx4.c
index 61a852fb9..4016ddb7b 100644
--- a/drivers/net/mlx4/mlx4.c
+++ b/drivers/net/mlx4/mlx4.c
@@ -741,11 +741,52 @@ static struct rte_pci_driver mlx4_driver = {
 static int
 mlx4_glue_init(void)
 {
+	const char *path[] = {
+		/*
+		 * A basic security check is necessary before trusting
+		 * MLX4_GLUE_PATH, which may override RTE_EAL_PMD_PATH.
+		 */
+		(geteuid() == getuid() && getegid() == getgid() ?
+		 getenv("MLX4_GLUE_PATH") : NULL),
+		RTE_EAL_PMD_PATH,
+	};
+	unsigned int i = 0;
 	void *handle = NULL;
 	void **sym;
 	const char *dlmsg;
 
-	handle = dlopen(MLX4_GLUE, RTLD_LAZY);
+	while (!handle && i != RTE_DIM(path)) {
+		const char *end;
+		size_t len;
+		int ret;
+
+		if (!path[i]) {
+			++i;
+			continue;
+		}
+		end = strpbrk(path[i], ":;");
+		if (!end)
+			end = path[i] + strlen(path[i]);
+		len = end - path[i];
+		ret = 0;
+		do {
+			char name[ret + 1];
+
+			ret = snprintf(name, sizeof(name), "%.*s%s" MLX4_GLUE,
+				       (int)len, path[i],
+				       (!len || *(end - 1) == '/') ? "" : "/");
+			if (ret == -1)
+				break;
+			if (sizeof(name) != (size_t)ret + 1)
+				continue;
+			DEBUG("looking for rdma-core glue as \"%s\"", name);
+			handle = dlopen(name, RTLD_LAZY);
+			break;
+		} while (1);
+		path[i] = end + 1;
+		if (!*end)
+			++i;
+	}
 	if (!handle) {
 		rte_errno = EINVAL;
 		dlmsg = dlerror();
diff --git a/drivers/net/mlx5/mlx5.c b/drivers/net/mlx5/mlx5.c
index 341230d2b..d1441dcba 100644
--- a/drivers/net/mlx5/mlx5.c
+++ b/drivers/net/mlx5/mlx5.c
@@ -1085,11 +1085,52 @@ static struct rte_pci_driver mlx5_driver = {
 static int
 mlx5_glue_init(void)
 {
+	const char *path[] = {
+		/*
+		 * A basic security check is necessary before trusting
+		 * MLX5_GLUE_PATH, which may override RTE_EAL_PMD_PATH.
+		 */
+		(geteuid() == getuid() && getegid() == getgid() ?
+		 getenv("MLX5_GLUE_PATH") : NULL),
+		RTE_EAL_PMD_PATH,
+	};
+	unsigned int i = 0;
 	void *handle = NULL;
 	void **sym;
 	const char *dlmsg;
 
-	handle = dlopen(MLX5_GLUE, RTLD_LAZY);
+	while (!handle && i != RTE_DIM(path)) {
+		const char *end;
+		size_t len;
+		int ret;
+
+		if (!path[i]) {
+			++i;
+			continue;
+		}
+		end = strpbrk(path[i], ":;");
+		if (!end)
+			end = path[i] + strlen(path[i]);
+		len = end - path[i];
+		ret = 0;
+		do {
+			char name[ret + 1];
+
+			ret = snprintf(name, sizeof(name), "%.*s%s" MLX5_GLUE,
+				       (int)len, path[i],
+				       (!len || *(end - 1) == '/') ? "" : "/");
+			if (ret == -1)
+				break;
+			if (sizeof(name) != (size_t)ret + 1)
+				continue;
+			DEBUG("looking for rdma-core glue as \"%s\"", name);
+			handle = dlopen(name, RTLD_LAZY);
+			break;
+		} while (1);
+		path[i] = end + 1;
+		if (!*end)
+			++i;
+	}
 	if (!handle) {
 		rte_errno = EINVAL;
 		dlmsg = dlerror();
-- 
2.11.0