mirror of
https://sourceware.org/git/glibc.git
synced 2024-12-23 11:20:07 +00:00
65eff7fbdb
Since commit 8b9e9c3c0b, security_level replaces
is_secure. There were some old files need to be updated.
2017-03-23 Sunyeop Lee <sunyeop97@gmail.com>
* README.tunables: Updated descriptions.
* elf/dl-tunables.list: Fixed typo: SXID_NONE -> NONE.
* scripts/gen-tunables.awk: Updated the code related to the commit.
86 lines
2.9 KiB
Plaintext
86 lines
2.9 KiB
Plaintext
TUNABLE FRAMEWORK
|
|
=================
|
|
|
|
Tunables is a feature in the GNU C Library that allows application authors and
|
|
distribution maintainers to alter the runtime library behaviour to match their
|
|
workload.
|
|
|
|
The tunable framework allows modules within glibc to register variables that
|
|
may be tweaked through an environment variable. It aims to enforce a strict
|
|
namespace rule to bring consistency to naming of these tunable environment
|
|
variables across the project. This document is a guide for glibc developers to
|
|
add tunables to the framework.
|
|
|
|
ADDING A NEW TUNABLE
|
|
--------------------
|
|
|
|
The TOP_NAMESPACE macro is defined by default as 'glibc'. If distributions
|
|
intend to add their own tunables, they should do so in a different top
|
|
namespace by overriding the TOP_NAMESPACE macro for that tunable. Downstream
|
|
implementations are discouraged from using the 'glibc' top namespace for
|
|
tunables they don't already have consensus to push upstream.
|
|
|
|
There are two steps to adding a tunable:
|
|
|
|
1. Add a tunable ID:
|
|
|
|
Modules that wish to use the tunables interface must define the
|
|
TUNABLE_NAMESPACE macro. Following this, for each tunable you want to
|
|
add, make an entry in elf/dl-tunables.list. The format of the file is as
|
|
follows:
|
|
|
|
TOP_NAMESPACE {
|
|
NAMESPACE1 {
|
|
TUNABLE1 {
|
|
# tunable attributes, one per line
|
|
}
|
|
# A tunable with default attributes, i.e. string variable.
|
|
TUNABLE2
|
|
TUNABLE3 {
|
|
# its attributes
|
|
}
|
|
}
|
|
NAMESPACE2 {
|
|
...
|
|
}
|
|
}
|
|
|
|
The list of allowed attributes are:
|
|
|
|
- type: Data type. Defaults to STRING. Allowed types are:
|
|
INT_32, SIZE_T and STRING.
|
|
|
|
- minval: Optional minimum acceptable value. For a string type
|
|
this is the minimum length of the value.
|
|
|
|
- maxval: Optional maximum acceptable value. For a string type
|
|
this is the maximum length of the value.
|
|
|
|
- env_alias: An alias environment variable
|
|
|
|
- security_level: Specify security level of the tunable. Valid values:
|
|
|
|
SXID_ERASE: (default) Don't read for AT_SECURE binaries and
|
|
removed so that child processes can't read it.
|
|
SXID_IGNORE: Don't read for AT_SECURE binaries, but retained for
|
|
non-AT_SECURE subprocesses.
|
|
NONE: Read all the time.
|
|
|
|
2. Call either the TUNABLE_SET_VALUE and pass into it the tunable name and a
|
|
pointer to the variable that should be set with the tunable value.
|
|
If additional work needs to be done after setting the value, use the
|
|
TUNABLE_SET_VALUE_WITH_CALLBACK instead and additionally pass a pointer to
|
|
the function that should be called if the tunable value has been set.
|
|
|
|
FUTURE WORK
|
|
-----------
|
|
|
|
The framework currently only allows a one-time initialization of variables
|
|
through environment variables and in some cases, modification of variables via
|
|
an API call. A future goals for this project include:
|
|
|
|
- Setting system-wide and user-wide defaults for tunables through some
|
|
mechanism like a configuration file.
|
|
|
|
- Allow tweaking of some tunables at runtime
|