Refactor VirtIO MMIO register map handling

[shengwen-tw]

Two adjustments are conducted in this pull request:

1. Replace the hard-coded register address checking with enum.
2. Handle the configuration space read / write with device-specific structures.

[jserv]

Move virtio-net and virtio-blk specific structure definitions from virtio.h to dedicated C source files.

Apply the trick opaque pointer to hide the implementation details. That is, consider the following changes:

--- a/device.h
+++ b/device.h
@@ -144,14 +144,14 @@ typedef struct {
     /* queue config */
     uint32_t QueueSel;
     virtio_blk_queue_t queues[2];
-    /* device configuration */
-    struct virtio_blk_config config;
     /* status */
     uint32_t Status;
     uint32_t InterruptStatus;
     /* supplied by environment */
     uint32_t *ram;
     uint32_t *disk;
+    /* implementation-specific */
+    void *priv;
 } virtio_blk_state_t;
 
 void virtio_blk_read(vm_t *vm,
--- a/virtio-blk.c
+++ b/virtio-blk.c
@@ -21,6 +21,46 @@
 #define VBLK_QUEUE_NUM_MAX 1024
 #define VBLK_QUEUE (vblk->queues[vblk->QueueSel])
+
+#define PRIV(x) ((struct virtio_blk_config *) x->priv)
+
 static void virtio_blk_set_fail(virtio_blk_state_t *vblk)
 {
     vblk->Status |= VIRTIO_STATUS__DEVICE_NEEDS_RESET;
@@ -45,11 +85,11 @@ static void virtio_blk_update_status(virtio_blk_state_t *vblk, uint32_t status)
     /* Reset */
     uint32_t *ram = vblk->ram;
     uint32_t *disk = vblk->disk;
-    uint32_t capacity = vblk->config.capacity;
+    uint32_t capacity = PRIV(vblk)->capacity;
     memset(vblk, 0, sizeof(*vblk));
     vblk->ram = ram;
     vblk->disk = disk;
-    vblk->config.capacity = capacity;
+    PRIV(vblk)->capacity = capacity;
 }
 
 static void virtio_blk_write_handler(virtio_blk_state_t *vblk,

Of course, you have to allocate the necessary memory for the region pointed by priv member.

[shengwen-tw]

Should we also add destructor functions to clean up the allocated memory (i.e., vnet->priv and vblk->priv) explicitly even if the program will only be terminated by pressing Ctrl+A then X?

[jserv]

Should we also add destructor functions to clean up the allocated memory (i.e., vnet->priv and vblk->priv) explicitly even if the program will only be terminated by pressing Ctrl+A then X?

Yes, you can do it in next pull request(s).
Follow the way how kvm-host does.

[jserv]

Rebase the latest master branch and resolve the conflicts.

[jserv]

Improve the git commit message. This commit addresses the following:

1. Re-organizes the source structures to improve code organization and maintainability.
2. Introduces the use of opaque pointer for information hiding, enhancing encapsulation and abstraction.
3. Enforces mnemonic enums instead of numbers, enhancing code readability and maintainability.

By incorporating these changes, the codebase becomes more structured and easier to understand and maintain.

[jserv]

Rebase the latest master branch.

[jserv]

Thank @shengwen-tw for contributing!