test: store persistence files in RAM

On VM-based builders, the nvmem unittest was sometimes missing the
10-second deadline, likely being stuck in slow I/Os.
Try to move the persistent storage files used for flash 'emulation' on
host from the build directory to a RAM-backed filesystem in /dev/shm
in order to mitigate this bottleneck.

Store the new backing files in a path like:
/dev/shm/EC_persist__mnt_host_source_src_platform_ec_build_host_nvmem_nvmem.exe_flash
in order to keep the properties of the old system:
subsequent runs of the same build will use the same persistent storage
but 2 different trees won't mix up.

Signed-off-by: Vincent Palatin <vpalatin@chromium.org>

BRANCH=none
BUG=chromium:715011
TEST=make runtests
TEST=run the following command with and without this change:
'for i in 0 1 2 3 4 5 6 7 8 9 ; do time make run-nvmem ; done'
and see the average test time around 500 ms without the change
and around 320 ms with it on an idle and beefy workstation.

Change-Id: Ic2ff6511b81869171efc484ca805f8c0d6008595
Reviewed-on: https://chromium-review.googlesource.com/893380
Commit-Ready: Vincent Palatin <vpalatin@chromium.org>
Tested-by: Vincent Palatin <vpalatin@chromium.org>
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>
(cherry picked from commit 924d21d904b9f2c640ee5b0ccabcf78200456a0f)
Reviewed-on: https://chromium-review.googlesource.com/928121
Commit-Queue: Vincent Palatin <vpalatin@chromium.org>
Trybot-Ready: Vincent Palatin <vpalatin@chromium.org>

1 files changed, 22 insertions, 14 deletions

diff --git a/chip/host/persistence.c b/chip/host/persistence.c
index 4be2683bb1..dbd1ce812c 100644
--- a/chip/host/persistence.c
+++ b/chip/host/persistence.c
@@ -5,35 +5,43 @@
 
 /* Persistence module for emulator */
 
+#include <linux/limits.h>
 #include <unistd.h>
 #include <stdio.h>
 #include <string.h>
 
-#define BUF_SIZE 1024
-
 static void get_storage_path(char *out)
 {
-	char buf[BUF_SIZE];
+	char buf[PATH_MAX];
 	int sz;
+	char *current;
 
-	sz = readlink("/proc/self/exe", buf, BUF_SIZE);
+	sz = readlink("/proc/self/exe", buf, PATH_MAX - 1);
 	buf[sz] = '\0';
-	if (snprintf(out, BUF_SIZE, "%s_persist", buf) >= BUF_SIZE)
-		out[BUF_SIZE - 1] = '\0';
+
+	/* replace / by underscores in the path to get the shared memory name */
+	current = strchr(buf, '/');
+	while (current) {
+		*current = '_';
+		current = strchr(current, '/');
+	}
+
+	snprintf(out, PATH_MAX - 1, "/dev/shm/EC_persist_%s", buf);
+	out[PATH_MAX - 1] = '\0';
 }
 
 FILE *get_persistent_storage(const char *tag, const char *mode)
 {
-	char buf[BUF_SIZE];
-	char path[BUF_SIZE];
+	char buf[PATH_MAX];
+	char path[PATH_MAX];
 
 	/*
 	 * The persistent storage with tag 'foo' for test 'bar' would
 	 * be named 'bar_persist_foo'
 	 */
 	get_storage_path(buf);
-	if (snprintf(path, BUF_SIZE, "%s_%s", buf, tag) >= BUF_SIZE)
-		path[BUF_SIZE - 1] = '\0';
+	snprintf(path, PATH_MAX - 1, "%s_%s", buf, tag);
+	path[PATH_MAX - 1] = '\0';
 
 	return fopen(path, mode);
 }
@@ -45,12 +53,12 @@ void release_persistent_storage(FILE *ps)
 
 void remove_persistent_storage(const char *tag)
 {
-	char buf[BUF_SIZE];
-	char path[BUF_SIZE];
+	char buf[PATH_MAX];
+	char path[PATH_MAX];
 
 	get_storage_path(buf);
-	if (snprintf(path, BUF_SIZE, "%s_%s", buf, tag) >= BUF_SIZE)
-		path[BUF_SIZE - 1] = '\0';
+	snprintf(path, PATH_MAX - 1, "%s_%s", buf, tag);
+	path[PATH_MAX - 1] = '\0';
 
 	unlink(path);
 }