Filesystem driver

[MadZarx]

Hello.
I just want to implement a FS driver to at least be able to read or write in a file in an ISO or floppy image FS. How and where should I start?
My question may be kind of dumb but I'm willing to build a hybrid kernel and I need to load drivers from a location in disk or image. Someone tell me how can I have a FS driver for ISO or IMG?

[Nable]

ISO (if one mean iso9660 FS) is read-only FS (ok, there are some special cases but I don't think it's time to discuss them).
IMG is not a format at all, it's just a filename extension. *.IMG disk images can contain ~any FS, although FAT12 and EXT2 are most common for floppies.
So, you need some routines (functions) to read (and possible write) blocks (device-specific stuff it you want to work with real devices or just fread/fwrite functions if you're building an image) and routines to work with FS structures (http://wiki.osdev.org/FAT , http://wiki.osdev.org/Ext2)

[sortie]

Don't confuse filesystems (or filesystem drivers) with block devices (or block device drivers). The filesystem driver doesn't care how the data is stored physically (except for some performance hints).

[bluemoon]

I suggest you start with designing your first simple block device and FS and VFS interface, and implement a simple ram disk + simpleFS/FAT combo.

For example, for my design I got 5 entities: disk driver, disk, FS driver, volume, VFS

block devices got these functions:

Code: Select all

typedef struct DRIVER_DISK_{
    DRIVER  header;
    int      (*create) (struct DRIVER_DISK_* driver, struct HAL_DISK_* disk, const char* resource, int option);
    int      (*destroy)(struct DRIVER_DISK_* driver, struct HAL_DISK_* disk);

    int      (*ioctl)  (struct HAL_DISK_* disk, int req, ...);
    uint64_t (*read)   (struct HAL_DISK_* disk, void* buf, uint64_t block, uint64_t nblock);
    uint64_t (*write)  (struct HAL_DISK_* disk, const void* buf, uint64_t block, uint64_t nblock);
} DRIVER_DISK;

Implement the ram disk driver is just trivial memcpy().

Then, to design the FS layer you may consider the following POSIX alike functions (taken from my OS as an example):

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int      tablefs_init     (DRIVER* driver);
int      tablefs_fini     (DRIVER* driver);
int      tablefs_create   (DRIVER_VOLUME* driver, HAL_VOLUME* volume);
int      tablefs_destroy  (DRIVER_VOLUME* driver, HAL_VOLUME* volume);

int      tablefs_format   (HAL_VOLUME* volume);
int      tablefs_open     (HAL_VOLUME* volume, FS_FILE* file, const char* path);
int      tablefs_close    (HAL_VOLUME* volume, FS_FILE* file);
uint64_t tablefs_read     (HAL_VOLUME* volume, FS_FILE* file, void* buf, uint64_t block, uint64_t nblock);
uint64_t tablefs_write    (HAL_VOLUME* volume, FS_FILE* file, const void* buf, uint64_t block, uint64_t nblock);
int      tablefs_opendir  (HAL_VOLUME* volume, FS_DIR *dir, const char* path);
int      tablefs_closedir (HAL_VOLUME* volume, FS_DIR *dir);
int      tablefs_readdir  (HAL_VOLUME* volume, FS_DIR *dir, unsigned int index, FS_DIRENT* dirent);

Finally, design the VFS layer to group together multiple volumes/mount points - single root like unix or multiple drives...

Once you got a basic VFS-FS-DEVICE architecture implemented, you may think about implementing IDE/SATA disk driver and/or all the fancy features (and perhaps rewrite the whole stuff with better understandings).

* Note that the above design is greatly simplified and may not suitable for serious kernel.

[MadZarx]

Alright guys. I didn't know that first I should write the device driver. Okay there is some tutorials on the wiki about disks, bu which one should I read to be able to read from an ISO9660?

[egos]

I didn't know that first I should write the device driver.

As bluemoon said, you can write RAM/image-based disk driver. Or you can impement storage device (driver) interface in image manipulation tool first (and then implement FS driver interface and VFS interface).

which one should I read to be able to read from an ISO9660?

To be able to read from CD/DVD with ISO9660 read the following:
- ATA Spec. and description of ATAPI packets;
- PCI IDE/AHCI Spec.;
- ISO 9660 Spec. and description of some its extensions.

[MadZarx]

Thanks egos. Thank you all