Re: [PATCH 2/2] Initialize tunable list with the GLIBC_TUNABLES environment variable

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Sat, Jul 2, 2016 at 10:12 AM, Siddhesh Poyarekar
<siddhesh@sourceware.org> wrote:
> 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))

Can you add the length of name to tunable_list field and check
if the length matches first?

> +           {
> +             /* 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
>



-- 
H.J.