吴锦华 / 明鑫 : 用户态文件系统 ( FUSE ) 框架分析和实战

static struct fuse_operations hello_oper = {
    .getattr    = hello_getattr,
    .readdir    = hello_readdir,
    .open       = hello_open,
    .read       = hello_read,
};
 
int main(int argc, char *argv[])
{
    return fuse_main(argc, argv, &hello_oper, NULL);
}

# hello /mnt/
# cd /mnt/
# ls -l
total 0
-r--r--r--    1 root     root            13 Jan  1  1970 hello
# cat hello
Hello World!
# touch a
touch: a: Function not implemented
# echo 0 > hello
-sh: can't create hello: Permission denied
# mkdir x
mkdir: can't create directory 'x': Function not implemented

struct fuse_operations {
    int (*getattr) (const char *, struct stat *);
    int (*readlink) (const char *, char *, size_t);
    int (*getdir) (const char *, fuse_dirh_t, fuse_dirfil_t);
    int (*mknod) (const char *, mode_t, dev_t);
    int (*mkdir) (const char *, mode_t);
    int (*unlink) (const char *);
    int (*rmdir) (const char *);
    int (*symlink) (const char *, const char *);
    int (*rename) (const char *, const char *);
    int (*link) (const char *, const char *);
    int (*chmod) (const char *, mode_t);
    int (*chown) (const char *, uid_t, gid_t);
    int (*truncate) (const char *, off_t);
    int (*utime) (const char *, struct utimbuf *);
    int (*open) (const char *, struct fuse_file_info *);
    int (*read) (const char *, char *, size_t, off_t,
             struct fuse_file_info *);
    int (*write) (const char *, const char *, size_t, off_t,
             struct fuse_file_info *);
    int (*statfs) (const char *, struct statvfs *);
    int (*flush) (const char *, struct fuse_file_info *);
    int (*release) (const char *, struct fuse_file_info *);
    int (*fsync) (const char *, int, struct fuse_file_info *);
    int (*setxattr) (const char *, const char *, const char *, size_t, int);
    int (*getxattr) (const char *, const char *, char *, size_t);
    int (*listxattr) (const char *, char *, size_t);
    int (*removexattr) (const char *, const char *);
    int (*opendir) (const char *, struct fuse_file_info *);
    int (*readdir) (const char *, void *, fuse_fill_dir_t, off_t,
            struct fuse_file_info *);
    int (*releasedir) (const char *, struct fuse_file_info *);
    int (*fsyncdir) (const char *, int, struct fuse_file_info *);
    void *(*init) (struct fuse_conn_info *conn);
    void (*destroy) (void *);
    int (*access) (const char *, int);
    int (*create) (const char *, mode_t, struct fuse_file_info *);
    int (*ftruncate) (const char *, off_t, struct fuse_file_info *);
    int (*fgetattr) (const char *, struct stat *, struct fuse_file_info *);
    int (*lock) (const char *, struct fuse_file_info *, int cmd,
             struct flock *);
    int (*utimens) (const char *, const struct timespec tv[2]);
    int (*bmap) (const char *, size_t blocksize, uint64_t *idx);
    unsigned int flag_nullpath_ok:1;
    unsigned int flag_nopath:1;
    unsigned int flag_utime_omit_ok:1;
    unsigned int flag_reserved:29;
    int (*ioctl) (const char *, int cmd, void *arg,
              struct fuse_file_info *, unsigned int flags, void *data);
    int (*poll) (const char *, struct fuse_file_info *,
             struct fuse_pollhandle *ph, unsigned *reventsp);
    int (*write_buf) (const char *, struct fuse_bufvec *buf, off_t off,
              struct fuse_file_info *);
    int (*read_buf) (const char *, struct fuse_bufvec **bufp,
             size_t size, off_t off, struct fuse_file_info *);
    int (*flock) (const char *, struct fuse_file_info *, int op);
    int (*fallocate) (const char *, int, off_t, off_t,
              struct fuse_file_info *);
};

#strace hello /mnt/
…
open("/dev/fuse", O_RDWR|O_LARGEFILE)   = 3
…
mount("hello", "/mnt", "fuse.hello", MS_NOSUID|MS_NODEV, "fd=3,rootmode=40000,user_id=0,gr"...) = 0
…

sys_mount
|-> do_mount
       |-> do_new_mount
            |-> get_fs_type
            |-> vfs_kern_mount
                 |-> mount_fs
                      |-> type->mount() [fuse_mount]
                           |-> mount_nodev
                                |-> fuse_fill_super
                                     |-> file = fget(d.fd);
                                     |-> fc->sb = sb
                                     |-> sb->s_fs_info = fc
                                     |-> fud = fuse_dev_alloc(fc)
                                     |-> file->private_data = fud

 jinhuawu@UbuntuPC:~/buildroot$ make qemu_arm_vexpress_defconfig
#
# configuration written to /home/jinhuawu/buildroot/.config
#
jinhuawu@UbuntuPC:~/buildroot$ make

jinhuawu@UbuntuPC:~/buildroot/output/images$ ls
rootfs.ext2  vexpress-v2p-ca9.dtb  zImage

jinhuawu@UbuntuPC:~/buildroot/output/images$ ls
rootfs.ext2  vexpress-v2p-ca9.dtb  zImage
jinhuawu@UbuntuPC:~/buildroot/output/images$ qemu-system-arm -M vexpress-a9 -m 512M -nographic -append "root=/dev/mmcblk0 console=ttyAMA0" -kernel zImage -sd rootfs.ext2  -dtb vexpress-v2p-ca9.dtb

Welcome to Buildroot
buildroot login: root
# quotafs -h
Usage: quota --src source_dirctory --size quota_size mount_point [OPTIONS]
Mount a user space quota filesytem.
 
 -h, show fuse option help
 --src, the source dircotry is going to setup the quota
 --size, the size of the quota
# quotafs --src /var/ --size 1024000 /mnt/
# mount
/dev/root on / type ext2 (rw,relatime)
devtmpfs on /dev type devtmpfs (rw,relatime,size=256244k,nr_inodes=64061,mode=755)
proc on /proc type proc (rw,relatime)
devpts on /dev/pts type devpts (rw,relatime,gid=5,mode=620)
tmpfs on /dev/shm type tmpfs (rw,relatime,mode=777)
tmpfs on /tmp type tmpfs (rw,relatime)
tmpfs on /run type tmpfs (rw,nosuid,nodev,relatime,mode=755)
sysfs on /sys type sysfs (rw,relatime)
quotafs on /mnt type fuse.quotafs (rw,nosuid,nodev,relatime,user_id=0,group_id=0)
# cd /mnt/
# ls
cache       lock        run         tmp         used_size
lib         log         spool       total_size  www
# cat total_size
1024000
# cat used_size
492866
# dd if=/dev/zero of=test bs=1 count=1000
1000+0 records in
1000+0 records out
# cat used_size
493866