initial commit

condviewfs.c

@@ -0,0 +1,254 @@
+#define _GNU_SOURCE
+
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#define FUSE_USE_VERSION 317
+
+#include <fuse3/fuse.h>
+
+static char *progname;
+static int fd1, fd2;
+
+static int get_fd() {
+	pid_t pid = fork();
+	if (pid == -1) {
+		perror("fork");
+		exit(1);
+	}
+	if (pid == 0) {
+		execl(progname, progname, (char *) NULL);
+
+		exit(2);
+	}
+
+	int wstatus;
+	if (waitpid(pid, &wstatus, 0) == -1) {
+		perror("waitpid");
+		exit(1);
+	}
+
+	int code = WEXITSTATUS(wstatus);
+	if (code == 0) return fd1;
+	if (code == 1) return fd2;
+
+	return -1;
+}
+
+static int condviewfs_open(const char *name, struct fuse_file_info *fi) {
+	int dirfd = get_fd();
+	if (dirfd == -1)
+		return -ENOLINK;
+
+	int fd = openat(dirfd, &name[1], fi->flags);
+	if (fd < 0)
+		return -errno;
+
+	fi->fh = (uint64_t)fd;
+	return 0;
+}
+
+static int condviewfs_close(const char *name, struct fuse_file_info *fi) {
+	if (close((int)fi->fh))
+		return -errno;
+
+	return 0;
+}
+
+static int condviewfs_getattr(const char *name,
+                        struct stat *stbuf,
+                        struct fuse_file_info *fi) {
+	int dirfd = get_fd();
+	if (dirfd == -1)
+		return -ENOLINK;
+
+	int ret;
+
+	if (fi)
+		ret = fstat((int)fi->fh, stbuf);
+	else
+		ret = fstatat(dirfd,
+	                  &name[1],
+	                  stbuf,
+	                  AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW);
+
+	if (ret < 0)
+		return -errno;
+
+	return 0;
+}
+
+static int condviewfs_access(const char *name, int mask) {
+	int dirfd = get_fd();
+	if (dirfd == -1)
+		return -ENOLINK;
+
+	if ((name[0] != '/') || (name[1] != '\0'))
+		++name;
+
+	if (faccessat(dirfd, name, mask, AT_SYMLINK_NOFOLLOW) < 0)
+		return -errno;
+
+	return 0;
+}
+
+static int condviewfs_read(const char *path,
+                     char *buf,
+                     size_t size,
+                     off_t off,
+                     struct fuse_file_info *fi) {
+	ssize_t out;
+
+	out = pread((int)fi->fh, buf, size > INT_MAX ? INT_MAX : size, off);
+	if (out < 0)
+		return -errno;
+
+	return (int)out;
+}
+
+static int condviewfs_opendir(const char *name, struct fuse_file_info *fi) {
+	DIR *dirp;
+	int dirfd = get_fd();
+	if (dirfd == -1)
+		return -ENOLINK;
+
+	int fd, err;
+
+	if ((name[0] == '/') && (name[1] == '\0'))
+		fd = dup(dirfd);
+	else
+		fd = openat(dirfd, &name[1], O_DIRECTORY);
+
+	if (fd < 0)
+		return -errno;
+
+	dirp = fdopendir(fd);
+	if (!dirp) {
+		err = -errno;
+		close(fd);
+		return err;
+	}
+
+	fi->fh = (uint64_t)dirp;
+	return 0;
+}
+
+static int condviewfs_closedir(const char *name, struct fuse_file_info *fi) {
+	if (closedir((DIR *)(uintptr_t)fi->fh) < 0)
+		return -errno;
+
+	return 0;
+}
+
+static int condviewfs_readdir(const char *path,
+                        void *buf,
+                        fuse_fill_dir_t filler,
+                        off_t offset,
+                        struct fuse_file_info *fi,
+                        enum fuse_readdir_flags flags) {
+	int dirfd = get_fd();
+	if (dirfd == -1)
+		return -ENOLINK;
+
+	DIR *dirp = (DIR *)(uintptr_t)fi->fh;
+
+	if (offset == 0)
+		rewinddir(dirp);
+
+	struct stat stbuf;
+	struct dirent *dent;
+	while (1) {
+		errno = 0;
+		dent = readdir(dirp);
+		if (!dent) {
+			if (errno == 0)
+				break;
+			return -errno;
+		}
+
+		if (fstatat(dirfd,
+		            dent->d_name,
+		            &stbuf,
+		            AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW) < 0)
+			return -errno;
+
+		if (filler(buf, dent->d_name, &stbuf, 0, FUSE_FILL_DIR_DEFAULTS) == 1) {
+			return -errno;
+		}
+	}
+
+	return 0;
+}
+
+static int condviewfs_readlink(const char *name, char *buf, size_t size) {
+	int dirfd = get_fd();
+	if (dirfd == -1)
+		return -ENOLINK;
+
+	ssize_t len;
+
+	len = readlinkat(dirfd,
+	                 &name[1],
+	                 buf,
+	                 size - 1);
+	if (len < 0)
+		return -errno;
+
+	buf[len] = '\0';
+	return 0;
+}
+
+static struct fuse_operations condviewfs_oper = {
+	.open		= condviewfs_open,
+	.release	= condviewfs_close,
+
+	.read		= condviewfs_read,
+
+	.getattr	= condviewfs_getattr,
+	.access		= condviewfs_access,
+
+	.opendir	= condviewfs_opendir,
+	.releasedir	= condviewfs_closedir,
+	.readdir	= condviewfs_readdir,
+
+	.readlink	= condviewfs_readlink,
+};
+
+int main(int argc, char *argv[]) {
+	char *fuse_argv[5];
+
+	if (argc != 5) {
+		fprintf(stderr, "Usage: %s target dir1 dir2 prog\n", argv[0]);
+		exit(-1);
+	}
+
+	fd1 = open(argv[2], O_DIRECTORY);
+	if (fd1 < 0) {
+		perror("open 1");
+		exit(-1);
+	}
+
+	fd2 = open(argv[3], O_DIRECTORY);
+	if (fd2 < 0) {
+		perror("open 2");
+		exit(-1);
+	}
+
+	progname = argv[4];
+
+	fuse_argv[0] = argv[0];
+	fuse_argv[1] = argv[1];
+	fuse_argv[2] = "-oallow_other,default_permissions";
+	fuse_argv[3] = "-f";
+	fuse_argv[4] = NULL;
+	return fuse_main(4, fuse_argv, &condviewfs_oper, NULL);
+}