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https://github.com/torvalds/linux
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fca5e94921
Even after commitc624adc9cb("samples: fix binderfs sample"), this sample is never compiled. 'hostprogs' teaches Kbuild that this is a host program, but not enough to order to compile it. You must add it to 'always-y' to really compile it. Since this sample has never been compiled in upstream, various issues are left unnoticed. [1] compilers without <linux/android/binderfs.h> are still widely used <linux/android/binderfs.h> is only available since commitc13295ad21("binderfs: rename header to binderfs.h"), i.e., Linux 5.0 If your compiler is based on UAPI headers older than Linux 5.0, you will see the following error: samples/binderfs/binderfs_example.c:16:10: fatal error: linux/android/binderfs.h: No such file or directory #include <linux/android/binderfs.h> ^~~~~~~~~~~~~~~~~~~~~~~~~~ compilation terminated. You cannot rely on compilers having such a new header. The common approach is to install UAPI headers of this kernel into usr/include, and then add it to the header search path. I added 'depends on HEADERS_INSTALL' in Kconfig, and '-I usr/include' compiler flag in Makefile. [2] compile the sample for target architecture Because headers_install works for the target architecture, only the native compiler was able to build sample code that requires '-I usr/include'. Commit7f3a59db27("kbuild: add infrastructure to build userspace programs") added the new syntax 'userprogs' to compile user-space programs for the target architecture. Use it, and then 'ifndef CROSS_COMPILE' will go away. I added 'depends on CC_CAN_LINK' because $(CC) is not necessarily capable of linking user-space programs. [3] use subdir-y to descend into samples/binderfs Since this directory does not contain any kernel-space code, it has no point in generating built-in.a or modules.order. Replace obj-$(CONFIG_...) with subdir-$(CONFIG_...). [4] -Wunused-variable warning If I compile this, I see the following warning. samples/binderfs/binderfs_example.c: In function 'main': samples/binderfs/binderfs_example.c:21:9: warning: unused variable 'len' [-Wunused-variable] 21 | size_t len; | ^~~ I removed the unused 'len'. [5] CONFIG_ANDROID_BINDERFS is not required Since this is a user-space standalone program, it is independent of the kernel configuration. Remove 'depends on ANDROID_BINDERFS'. Fixes:9762dc1432("samples: add binderfs sample program") Fixes:c624adc9cb("samples: fix binderfs sample") Signed-off-by: Masahiro Yamada <masahiroy@kernel.org> Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
83 lines
1.9 KiB
C
83 lines
1.9 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#define _GNU_SOURCE
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#include <errno.h>
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#include <fcntl.h>
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#include <sched.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sys/ioctl.h>
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#include <sys/mount.h>
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#include <sys/stat.h>
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#include <sys/types.h>
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#include <unistd.h>
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#include <linux/android/binder.h>
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#include <linux/android/binderfs.h>
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int main(int argc, char *argv[])
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{
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int fd, ret, saved_errno;
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struct binderfs_device device = { 0 };
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ret = unshare(CLONE_NEWNS);
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if (ret < 0) {
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fprintf(stderr, "%s - Failed to unshare mount namespace\n",
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strerror(errno));
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exit(EXIT_FAILURE);
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}
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ret = mount(NULL, "/", NULL, MS_REC | MS_PRIVATE, 0);
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if (ret < 0) {
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fprintf(stderr, "%s - Failed to mount / as private\n",
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strerror(errno));
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exit(EXIT_FAILURE);
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}
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ret = mkdir("/dev/binderfs", 0755);
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if (ret < 0 && errno != EEXIST) {
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fprintf(stderr, "%s - Failed to create binderfs mountpoint\n",
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strerror(errno));
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exit(EXIT_FAILURE);
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}
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ret = mount(NULL, "/dev/binderfs", "binder", 0, 0);
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if (ret < 0) {
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fprintf(stderr, "%s - Failed to mount binderfs\n",
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strerror(errno));
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exit(EXIT_FAILURE);
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}
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memcpy(device.name, "my-binder", strlen("my-binder"));
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fd = open("/dev/binderfs/binder-control", O_RDONLY | O_CLOEXEC);
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if (fd < 0) {
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fprintf(stderr, "%s - Failed to open binder-control device\n",
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strerror(errno));
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exit(EXIT_FAILURE);
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}
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ret = ioctl(fd, BINDER_CTL_ADD, &device);
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saved_errno = errno;
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close(fd);
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errno = saved_errno;
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if (ret < 0) {
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fprintf(stderr, "%s - Failed to allocate new binder device\n",
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strerror(errno));
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exit(EXIT_FAILURE);
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}
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printf("Allocated new binder device with major %d, minor %d, and name %s\n",
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device.major, device.minor, device.name);
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ret = unlink("/dev/binderfs/my-binder");
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if (ret < 0) {
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fprintf(stderr, "%s - Failed to delete binder device\n",
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strerror(errno));
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exit(EXIT_FAILURE);
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}
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/* Cleanup happens when the mount namespace dies. */
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exit(EXIT_SUCCESS);
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}
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