Writing a simple filesystem in C using FUSE

Question

I've learned the hello.c. It can create a hello file under mountfile. But I've no idea about how to create a folder under the mountfile and then create hello under mountfile/folderIcreate. then I can use cat mountfile/folderIcreate/hello the code is similar to the simple hello.c

#define FUSE_USE_VERSION 30

#include <fuse.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>

static const char *hello_str = "Hello World!\n";
static const char *add_path = "/add";
static const char *div_path = "/div";
static const char *hello_path = "/hello";

static int hello_getattr(const char *path, struct stat *stbuf)
{
    int res = 0;

    printf("%s", path);

    memset(stbuf, 0, sizeof(struct stat));
    if (strcmp(path, "/") == 0) 
    {
        stbuf->st_mode = S_IFDIR | 0755;
        stbuf->st_nlink = 2;
    } 
    else if (strcmp(path, hello_path) == 0) 
    {
        stbuf->st_mode = S_IFREG | 0444;
        stbuf->st_nlink = 1;
        stbuf->st_size = strlen(hello_str);
    }
    else if (strcmp(path, add_path) == 0) 
    {
        stbuf->st_mode = S_IFDIR | 0755;
        stbuf->st_nlink = 3;
        if (strcmp(path, add_path1) == 0) 
        {
            stbuf->st_mode = S_IFREG | 0444;
            stbuf->st_nlink = 1;
            stbuf->st_size = strlen(hello_str);
        }
    }
    else if(strcmp(path, div_path) == 0)
    {
        stbuf->st_mode = S_IFDIR | 0755;
        stbuf->st_nlink = 3;
    } 
    else if(strcmp(path, div_path) == 0)
    {
        stbuf->st_mode = S_IFDIR | 0755;
        stbuf->st_nlink = 3;
    } 
    else
        res = -ENOENT;

    return res;
}

static int hello_readdir(const char *path, void *buf, fuse_fill_dir_t filler,
         off_t offset, struct fuse_file_info *fi)
{
    printf("%s", path);
    (void) offset;
    (void) fi;

    if (strcmp(path, "/") != 0)
        return -ENOENT;

    filler(buf, ".", NULL, 0);
    filler(buf, "..", NULL, 0);
    filler(buf, hello_path + 1, NULL, 0);
    filler(buf, add_path + 1, NULL, 0);
    filler(buf, div_path + 1, NULL, 0);

    return 0;
}

static int hello_open(const char *path, struct fuse_file_info *fi)
{
    printf("%s", path);
    if (strcmp(path, hello_path) != 0)
        return -ENOENT;

    if ((fi->flags & 3) != O_RDONLY)
        return -EACCES;

    return 0;
}

static int hello_read(const char *path, char *buf, size_t size, off_t offset,
          struct fuse_file_info *fi)
{
    printf("%s", path);
    size_t len;
    (void) fi;
    if(strcmp(path, hello_path) != 0)
        return -ENOENT;

    len = strlen(hello_str);
    if (offset < len) {
        if (offset + size > len)
            size = len - offset;
        memcpy(buf, hello_str + offset, size);
    } else
        size = 0;

    return size;
}

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);
}

can someone give a simple example about how to revise the code above without changing the struct fuse_operations. Thank you!

Answer 1

To make a directory work properly in a FUSE filesystem, the following conditions need to be met:

• The directory needs to be stat()-able, and should return properties appropriate for a directory (e.g, readable, executable, and S_IFDIR).

• The directory needs to be readdir()-able.

• The directory needs to appear in a readdir() listing of its parent. (This is somewhat optional, but having the directory not appear in a listing is unusual, and will make it difficult to access!)

• Any new paths under the directory need to be stat()able and open()/read()able if appropriate.

None of these are new operations; they're just extensions of existing ones. If there are specific questions you have about how to make some of these changes, please clarify your question.