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With the recent changes to bypass loading the file it's possible to
reduce the work in userspace and delegating it to the kernel. Without
any compression to illustrate:
Before:
read(3, "\177ELF\2\1", 6) = 6
lseek(3, 0, SEEK_SET) = 0
newfstatat(3, "", {st_mode=S_IFREG|0644, st_size=238592, ...}, AT_EMPTY_PATH) = 0
mmap(NULL, 238592, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fd85cbd1000
finit_module(3, "", 0) = 0
munmap(0x7fd85cbd1000, 238592) = 0
close(3) = 0
After:
read(3, "\177ELF\2\1", 6) = 6
lseek(3, 0, SEEK_SET) = 0
finit_module(3, "", 0) = 0
close(3) = 0
When using kernel compression now it's also possible to direct libkmod
to take the finit_module() path, avoiding the decompression in userspace
and just delegating it to the kernel.
Before:
read(3, "(\265/\375\244\0", 6) = 6
lseek(3, 0, SEEK_SET) = 0
read(3, "(\265/\375\244", 5) = 5
mmap(NULL, 135168, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3fa431e000
read(3, "\0\244\3\0\\y\6", 7) = 7
mmap(NULL, 372736, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3fa414f000
brk(0x55944c6a1000) = 0x55944c6a1000
read(3, "\356|\6G\27U\20 \312\260s\211\335\333\263\326\330\336\273O\211\356\306K\360Z\341\374U6\342\221"..., 53038) = 53038
mremap(0x7f3fa431e000, 135168, 266240, MREMAP_MAYMOVE) = 0x7f3fa410e000
read(3, ",;\3\nqf\311\362\325\211\7\341\375A\355\221\371L\\\5\7\375 \32\246<(\258=K\304"..., 20851) = 20851
mremap(0x7f3fa410e000, 266240, 397312, MREMAP_MAYMOVE) = 0x7f3fa40ad000
read(3, ")\36\250\213", 4) = 4
read(3, "", 4) = 0
munmap(0x7f3fa414f000, 372736) = 0
init_module(0x7f3fa40ad010, 238592, "") = 0
munmap(0x7f3fa40ad000, 397312) = 0
close(3) = 0
After:
read(3, "(\265/\375\244P", 6) = 6
lseek(3, 0, SEEK_SET) = 0
finit_module(3, "", 0x4 /* MODULE_INIT_??? */) = 0
close(3) = 0
Signed-off-by: Lucas De Marchi <lucas.de.marchi@gmail.com>
libkmod - linux kernel module handling library
ABSTRACT
========
libkmod was created to allow programs to easily insert, remove and
list modules, also checking its properties, dependencies and aliases.
there is no shared/global context information and it can be used by
multiple sites on a single program, also being able to be used from
threads, although it's not thread safe (you must lock explicitly).
OVERVIEW
========
Every user should create and manage it's own library context with:
struct kmod_ctx *ctx = kmod_new(kernel_dirname);
kmod_unref(ctx);
Modules can be created by various means:
struct kmod_module *mod;
int err;
err = kmod_module_new_from_path(ctx, path, &mod);
if (err < 0) {
/* code */
} else {
/* code */
kmod_module_unref(mod);
}
err = kmod_module_new_from_name(ctx, name, &mod);
if (err < 0) {
/* code */
} else {
/* code */
kmod_module_unref(mod);
}
Or could be resolved from a known alias to a list of alternatives:
struct kmod_list *list, *itr;
int err;
err = kmod_module_new_from_lookup(ctx, alias, &list);
if (err < 0) {
/* code */
} else {
kmod_list_foreach(itr, list) {
struct kmod_module *mod = kmod_module_get_module(itr);
/* code */
}
}