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readme: add more detail to limitations section

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Josh Poimboeuf 2014-03-21 14:57:52 -05:00
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README.md
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@ -144,18 +144,32 @@ function's arguments and stack, and "returns" to the new function.
Limitations
-----------
- kpatch can't detect when a patch changes the contents of a dynamically
allocated data structure, and isn't able to determine whether such patches
are safe to apply. It's the user's responsibility to analyze any such
patches for safety before applying them.
- Patches which change the contents of static data structures are not currently
supported. kpatch-build will detect such changes and report an error.
- Patches to functions which are always in the call stack of a task, such as
schedule(), will fail to apply at runtime.
- Patches which change functions that are only called in the kernel init path
will have no effect (obviously).
- Currently, kernel module functions can't be patched -- only functions in the
base kernel image.
- Patches which modify kernel modules are not supported (yet). Only
functions in the vmlinux file (listed in System.map) can be patched.
- Patches to functions which are always on the stack of at least one
process in the system are not supported. Examples: schedule(),
sys_poll(), sys_select(), sys_read(), sys_nanosleep(). Attempting to
apply such a patch will cause the insmod of the patch module to return
an error.
- Patches which modify init functions (annotated with `__init`) are not
supported. kpatch-build will return an error if the patch attempts
to do so.
- Patches which modify statically allocated data are not supported.
kpatch-build will detect that and return an error. (In the future
we will add a facility to support it. It will probably require the
user to write code which runs at module loading time which manually
updates the data.)
- Patches which change the way a function interacts with dynamically
allocated data might be safe, or might not. It isn't possible for
kpatch-build to verify the safety of this kind of patch. It's up to
the user to understand what the patch does, whether the new functions
interact with dynamically allocated data in a different way than the
old functions did, and whether it would be safe to atomically apply
such a patch to a running kernel.
Frequently Asked Questions