[dpdk-dev] [PATCH] eal: avoid unnecessary conflicts over rte_config file

[John Ousterhout <ouster@cs.stanford.edu>]

Before this patch, DPDK used the file ~/.rte_config as a lock to detect
potential interference between multiple DPDK applications running on the
same machine. However, if a single user ran DPDK applications concurrently
on several different machines, and if the user's home directory was shared
between the machines via NFS, DPDK would incorrectly detect conflicts
for all but the first application and abort them. This patch fixes the
problem by incorporating the machine name into the config file name (e.g.,
~/.rte_hostname_config).

Signed-off-by: John Ousterhout <ouster@cs.stanford.edu>
---
 doc/guides/prog_guide/multi_proc_support.rst | 11 +++++++----
 lib/librte_eal/common/eal_common_proc.c      |  8 ++------
 lib/librte_eal/common/eal_filesystem.h       | 15 +++++++++++++--
 3 files changed, 22 insertions(+), 12 deletions(-)

diff --git a/doc/guides/prog_guide/multi_proc_support.rst b/doc/guides/prog_guide/multi_proc_support.rst
index badd102..a54fa1c 100644
--- a/doc/guides/prog_guide/multi_proc_support.rst
+++ b/doc/guides/prog_guide/multi_proc_support.rst
@@ -129,10 +129,13 @@ Support for this usage scenario is provided using the ``--file-prefix`` paramete
 
 By default, the EAL creates hugepage files on each hugetlbfs filesystem using the rtemap_X filename,
 where X is in the range 0 to the maximum number of hugepages -1.
-Similarly, it creates shared configuration files, memory mapped in each process, using the /var/run/.rte_config filename,
-when run as root (or $HOME/.rte_config when run as a non-root user;
-if filesystem and device permissions are set up to allow this).
-The rte part of the filenames of each of the above is configurable using the file-prefix parameter.
+Similarly, it creates shared configuration files, memory mapped in each process.
+When run as root, the name of the configuration file will be
+/var/run/.rte_*host*_config, where *host* is the name of the machine.
+When run as a non-root user, the the name of the configuration file will be
+$HOME/.rte_*host*_config (if filesystem and device permissions are set up to allow this).
+If the ``--file-prefix`` parameter has been specified, its value will be used
+in place of "rte" in the file names.
 
 In addition to specifying the file-prefix parameter,
 any DPDK applications that are to be run side-by-side must explicitly limit their memory use.
diff --git a/lib/librte_eal/common/eal_common_proc.c b/lib/librte_eal/common/eal_common_proc.c
index 12e0fca..517aa0c 100644
--- a/lib/librte_eal/common/eal_common_proc.c
+++ b/lib/librte_eal/common/eal_common_proc.c
@@ -45,12 +45,8 @@ rte_eal_primary_proc_alive(const char *config_file_path)
 
 	if (config_file_path)
 		config_fd = open(config_file_path, O_RDONLY);
-	else {
-		char default_path[PATH_MAX+1];
-		snprintf(default_path, PATH_MAX, RUNTIME_CONFIG_FMT,
-			 default_config_dir, "rte");
-		config_fd = open(default_path, O_RDONLY);
-	}
+	else
+		config_fd = open(eal_runtime_config_path(), O_RDONLY);
 	if (config_fd < 0)
 		return 0;
 
diff --git a/lib/librte_eal/common/eal_filesystem.h b/lib/librte_eal/common/eal_filesystem.h
index fdb4a70..4929aa3 100644
--- a/lib/librte_eal/common/eal_filesystem.h
+++ b/lib/librte_eal/common/eal_filesystem.h
@@ -41,7 +41,7 @@
 #define EAL_FILESYSTEM_H
 
 /** Path of rte config file. */
-#define RUNTIME_CONFIG_FMT "%s/.%s_config"
+#define RUNTIME_CONFIG_FMT "%s/.%s_%s_config"
 
 #include <stdint.h>
 #include <limits.h>
@@ -59,11 +59,22 @@ eal_runtime_config_path(void)
 	static char buffer[PATH_MAX]; /* static so auto-zeroed */
 	const char *directory = default_config_dir;
 	const char *home_dir = getenv("HOME");
+	static char nameBuffer[1000];
+	int result;
 
 	if (getuid() != 0 && home_dir != NULL)
 		directory = home_dir;
+
+	/*
+	 * Include the name of the host in the config file path. Otherwise,
+	 * if DPDK applications run on different hosts but share a home
+	 * directory (e.g. via NFS), they will choose the same config
+	 * file and conflict unnecessarily.
+	 */
+	result = gethostname(nameBuffer, sizeof(nameBuffer)-1);
 	snprintf(buffer, sizeof(buffer) - 1, RUNTIME_CONFIG_FMT, directory,
-			internal_config.hugefile_prefix);
+			internal_config.hugefile_prefix,
+		(result == 0) ? nameBuffer : "unknown-host");
 	return buffer;
 }
 
-- 
2.8.3