example1-tmpfs.c

#include "common.h"

// Mount now happens in 5 steps:
// 1 - Create a filesystem context
// 2 - Configure
// 3 - Validate configuration
// 4 - Mount (detached)
// 5 - Attach to the filesystem


int main(void) {
    char mountpoint[255] = "tmpfs/";
    addcurpath(mountpoint);

    printpid();
    wait("* Step 1: Will create a filesystem context");
    int fscontext_fd = fsopen("tmpfs", 0);
    if (fscontext_fd < 0) {
        perror("fsopen failed");
        return 1;
    }
    printf("The file descriptor for the handle is fd %d\n", fscontext_fd);


    wait("* Step 2: Configuring the size to 50M...");
    if (fsconfig(fscontext_fd, FSCONFIG_SET_STRING, "size", "50M", 0) < 0) {
        perror("fsconfig size");
        return 1;
    }
    printf("Finished configuration\n");


    wait("* Step 3: Validate the configuration.");
    if (fsconfig(fscontext_fd, FSCONFIG_CMD_CREATE, NULL, NULL, 0) < 0) {
        perror("fsconfig create");
        return 1;
    }
    printf("Configuration is valid\n");


    wait("* Step 4: Mount");
    int mount_fd = fsmount(fscontext_fd, 0, 0);
    if (mount_fd < 0) {
        perror("fsmount");
        return 1;
    }
    printf("Mount successful. Mount fd is %d. Have a look at /proc/%d/fdinfo/%d\n", mount_fd, getpid(), mount_fd);


    wait("* Step 5: Move mount and make it visible");
    if (move_mount(mount_fd, "", AT_FDCWD, mountpoint, MOVE_MOUNT_F_EMPTY_PATH) < 0) {
        perror("move_mount");
        return 1;
    }
    printf("tmpfs is now visible at %s. Don't forget to umount!\n", mountpoint);


    close(fscontext_fd);
    close(mount_fd);
    return 0;
}