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[PATCH 2/2] Initialize tunable list with the GLIBC_TUNABLES environment variable
- From: Siddhesh Poyarekar <siddhesh at sourceware dot org>
- To: libc-alpha at sourceware dot org
- Date: Sat, 2 Jul 2016 00:01:18 +0530
- Subject: [PATCH 2/2] Initialize tunable list with the GLIBC_TUNABLES environment variable
- Authentication-results: sourceware.org; auth=none
- References: <1467397878-11514-1-git-send-email-siddhesh at sourceware dot org>
Read tunables values from the users using the GLIBC_TUNABLES
environment variable. The value of this variable is a colon-separated
list of name=value pairs. So a typical string would look like this:
GLIBC_TUNABLES=glibc.malloc.mmap_threshold=2048:glibc.malloc.trim_threshold=1024
* elf/dl-tunables.c: Include string.h.
(parse_tunables): New function.
(GLIBC_TUNABLES): New macro.
(__tunables_init): Use it.
---
elf/dl-tunables.c | 69 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 69 insertions(+)
diff --git a/elf/dl-tunables.c b/elf/dl-tunables.c
index 8a26dfc..04d1d52 100644
--- a/elf/dl-tunables.c
+++ b/elf/dl-tunables.c
@@ -22,10 +22,13 @@
#include <stdbool.h>
#include <unistd.h>
#include <stdlib.h>
+#include <string.h>
#define TUNABLES_INTERNAL 1
#include "dl-tunables.h"
+#define GLIBC_TUNABLES "GLIBC_TUNABLES"
+
/* Compare environment names, bounded by the name hardcoded in glibc. */
static bool
is_name (const char *orig, const char *envname)
@@ -104,6 +107,66 @@ tunable_initialize (tunable_t *cur)
}
}
+static void
+parse_tunables (char *tunestr)
+{
+ if (tunestr == NULL || *tunestr == '\0')
+ return;
+
+ char *p = tunestr;
+
+ while (true)
+ {
+ char *name = p;
+ size_t len = 0;
+
+ /* First, find where the name ends. */
+ while (p[len] != '=' && p[len] != ':' && p[len] != '\0')
+ len++;
+
+ /* If we reach the end of the string before getting a valid name-value
+ pair, bail out. */
+ if (p[len] == '\0')
+ return;
+
+ /* We did not find a valid name-value pair before encountering the
+ colon. */
+ if (p[len]== ':')
+ {
+ p += len + 1;
+ continue;
+ }
+
+ p += len + 1;
+
+ char *value = p;
+ len = 0;
+
+ while (p[len] != ':' && p[len] != '\0')
+ len++;
+
+ char end = p[len];
+ p[len] = '\0';
+
+ /* Add the tunable if it exists. */
+ for (size_t i = 0; i < sizeof (tunable_list) / sizeof (tunable_t); i++)
+ {
+ if (is_name (tunable_list[i].name, name))
+ {
+ /* Tunable values take precedence over the env_alias. */
+ tunable_list[i].strval = value;
+ tunable_initialize (&tunable_list[i]);
+ break;
+ }
+ }
+
+ if (end == ':')
+ p += len + 1;
+ else
+ return;
+ }
+}
+
/* Initialize the tunables list from the environment. For now we only use the
ENV_ALIAS to find values. Later we will also use the tunable names to find
values. */
@@ -116,6 +179,12 @@ __tunables_init (char **envp)
while (get_next_env (&envp, &envname, &len, &envval))
{
+ if (is_name (GLIBC_TUNABLES, envname))
+ {
+ parse_tunables (strdup (envval));
+ continue;
+ }
+
for (int i = 0; i < sizeof (tunable_list) / sizeof (tunable_t); i++)
{
tunable_t *cur = &tunable_list[i];
--
2.5.5