Implement virtio filesystem in semu

Map MMIO region at 0xF48____ for virtio-fs device in semu.
Introduce special-case logic for char tag in virtio_fs config handling in semu.
Add inode_map linked list for mapping inodes to file paths.
Implement FUSE core operations:
- INIT
- GETATTR
- OPENDIR
- READDIRPLUS
- LOOKUP
- FORGET
- RELEASEDIR
- OPEN
- READ
- RELEASE
- FLUSH
- DESTROY
to make semu supports commands:`cd`, `cat`, `ls`.
Set default mount tag to "myfs" and mount directory to "./shared".
When `make check`, if MOUNT_DIRECTORY is not exist, then create a new one.
If -s parameter is empty, virtio-fs is unused.
Add the explanation about virtio-fs in `Usage` of README.md.
Add the introduction of how to mount and unmount in semu.
When the guest OS attempts an unsupported operation, it should receive a "operation not supported" response instead of hanging to improve the user experience.

Co-authored-by: ChinYikMing <yikming2222@gmail.com>

Author: MikazukiHikari

Makefile

@@ -41,6 +41,15 @@ ifeq ($(call has, VIRTIORNG), 1)
     OBJS_EXTRA += virtio-rng.o
 endif
 
+# virtio-fs
+ENABLE_VIRTIOFS ?= 1
+$(call set-feature, VIRTIOFS)
+SHARED_DIRECTORY ?= ./shared
+ifeq ($(call has, VIRTIOFS), 1)
+    OBJS_EXTRA += virtio-fs.o
+    OPTS += -s $(SHARED_DIRECTORY)
+endif
+
 NETDEV ?= tap
 # virtio-net
 ENABLE_VIRTIONET ?= 1
@@ -214,7 +223,14 @@ ext4.img:
 	$(Q)dd if=/dev/zero of=$@ bs=4k count=600
 	$(Q)$(MKFS_EXT4) -F $@
 
-check: $(BIN) minimal.dtb $(KERNEL_DATA) $(INITRD_DATA) $(DISKIMG_FILE)
+.PHONY: $(DIRECTORY)
+$(SHARED_DIRECTORY):
+	@if [ ! -d $@ ]; then \
+		echo "Creating mount directory: $@"; \
+		mkdir -p $@; \
+	fi
+
+check: $(BIN) minimal.dtb $(KERNEL_DATA) $(INITRD_DATA) $(DISKIMG_FILE) $(SHARED_DIRECTORY)
 	@$(call notice, Ready to launch Linux kernel. Please be patient.)
 	$(Q)./$(BIN) -k $(KERNEL_DATA) -c $(SMP) -b minimal.dtb -i $(INITRD_DATA) -n $(NETDEV) $(OPTS)
 

README.md

@@ -77,13 +77,33 @@ You can exit the emulator using: \<Ctrl-a x\>. (press Ctrl+A, leave it, afterwar
 ## Usage
 
 ```shell
-./semu -k linux-image [-b dtb-file] [-i initrd-image] [-d disk-image]
+./semu -k linux-image [-b dtb-file] [-i initrd-image] [-d disk-image] [-s shared-directory]
 ```
 
 * `linux-image` is the path to the Linux kernel `Image`.
 * `dtb-file` is optional, as it specifies the user-specified device tree blob.
 * `initrd-image` is optional, as it specifies the user-specified initial RAM disk image.
 * `disk-image` is optional, as it specifies the path of a disk image in ext4 file system for the virtio-blk device.
+* `shared-directory` is optional, as it specifies the path of a directory on the host that will be shared with the guest operating system through virtio-fs, enabling file access from the guest via a virtual filesystem mount.
+
+## Mount and unmount a directory in semu
+
+To mount the directory in semu:
+
+```shell
+$ mount -t virtiofs myfs [shared-directory]
+```
+
+* `shared-directory` is the path of a directory you want to mount in semu.
+
+To unmount the directory in semu:
+
+```shell
+$ umount [shared-directory]
+```
+
+* `shared-directory` is the path of a directory you want to unmount in semu.
+
 
 ## Build Linux kernel image and root file system
 

device.h

@@ -357,6 +357,70 @@ void virtio_snd_write(hart_t *core,
 bool virtio_snd_init(virtio_snd_state_t *vsnd);
 #endif /* SEMU_HAS(VIRTIOSND) */
 
+/* VirtIO-File-System */
+
+#if SEMU_HAS(VIRTIOFS)
+#define IRQ_VFS 6
+#define IRQ_VFS_BIT (1 << IRQ_VFS)
+
+typedef struct inode_map_entry {
+    uint64_t ino;
+    char *path;
+    struct inode_map_entry *next;
+} inode_map_entry;
+
+typedef struct {
+    uint32_t QueueNum;
+    uint32_t QueueDesc;
+    uint32_t QueueAvail;
+    uint32_t QueueUsed;
+    uint16_t last_avail;
+    bool ready;
+} virtio_fs_queue_t;
+
+typedef struct {
+    /* feature negotiation */
+    uint32_t DeviceFeaturesSel;
+    uint32_t DriverFeatures;
+    uint32_t DriverFeaturesSel;
+
+    /* queue config */
+    uint32_t QueueSel;
+    virtio_fs_queue_t queues[3];
+
+    /* status */
+    uint32_t Status;
+    uint32_t InterruptStatus;
+
+    /* guest memory base */
+    uint32_t *ram;
+
+    char *mount_tag; /* guest sees this tag */
+    char *shared_dir;
+
+    inode_map_entry *inode_map;
+
+    /* optional implementation-specific */
+    void *priv;
+} virtio_fs_state_t;
+
+/* MMIO read/write */
+void virtio_fs_read(hart_t *core,
+                    virtio_fs_state_t *vfs,
+                    uint32_t addr,
+                    uint8_t width,
+                    uint32_t *value);
+
+void virtio_fs_write(hart_t *core,
+                     virtio_fs_state_t *vfs,
+                     uint32_t addr,
+                     uint8_t width,
+                     uint32_t value);
+
+bool virtio_fs_init(virtio_fs_state_t *vfs, char *mtag, char *dir);
+
+#endif /* SEMU_HAS(VIRTIOFS) */
+
 /* memory mapping */
 typedef struct {
     bool debug;
@@ -382,6 +446,9 @@ typedef struct {
 #if SEMU_HAS(VIRTIOSND)
     virtio_snd_state_t vsnd;
 #endif
+#if SEMU_HAS(VIRTIOFS)
+    virtio_fs_state_t vfs;
+#endif
 
     uint32_t peripheral_update_ctr;
 

feature.h

@@ -17,5 +17,10 @@
 #define SEMU_FEATURE_VIRTIOSND 1
 #endif
 
+/* virtio-fs */
+#ifndef SEMU_FEATURE_VIRTIOFS
+#define SEMU_FEATURE_VIRTIOFS 1
+#endif
+
 /* Feature test macro */
 #define SEMU_HAS(x) SEMU_FEATURE_##x

fuse.h

@@ -0,0 +1,159 @@
+#include "riscv.h"
+#include "virtio.h"
+
+#define FUSE_REC_ALIGN(x) \
+    (((x) + sizeof(uint64_t) - 1) & ~(sizeof(uint64_t) - 1))
+#define FUSE_DIRENT_ALIGN(x) FUSE_REC_ALIGN(x)
+
+struct fuse_in_header {
+    uint32_t len;
+    uint32_t opcode;
+    uint64_t unique;
+    uint64_t nodeid;
+    uint32_t uid;
+    uint32_t gid;
+    uint32_t pid;
+    uint32_t padding;
+};
+
+struct fuse_out_header {
+    uint32_t len;
+    int32_t error;
+    uint64_t unique;
+};
+
+struct vfs_req_header {
+    struct fuse_in_header in;
+};
+
+struct vfs_resp_header {
+    struct fuse_out_header out;
+};
+
+struct fuse_init_in {
+    /* FUSE major version supported by the guest (typically 7) */
+    uint32_t major;
+    /* FUSE minor version supported by the guest (e.g., 31, 26) */
+    uint32_t minor;
+    uint32_t max_readahead; /* Maximum readahead size supported by the guest */
+    uint32_t flags;         /* Flags requested by the guest */
+};
+
+struct fuse_init_out {
+    uint32_t major;         /* FUSE major version supported by the device */
+    uint32_t minor;         /* FUSE minor version supported by the device */
+    uint32_t max_readahead; /* Maximum readahead size accepted by the device */
+    /* Flags supported by the device (negotiated with the guest) */
+    uint32_t flags;
+    uint16_t max_background; /* Maximum number of background requests */
+    uint16_t congestion_threshold;
+    uint32_t max_write;  /* Maximum write size the device can handle */
+    uint32_t time_gran;  /* Time granularity (in nanoseconds) */
+    uint32_t unused[11]; /* Reserved */
+};
+
+struct fuse_getattr_in {
+    /* bitmask for valid fields (e.g. FUSE_GETATTR_FH) */
+    uint32_t getattr_flags;
+    uint32_t padding; /* unused, reserved for alignment */
+    uint64_t fh;      /* optional: file handle (used when getattr_flags has */
+};
+
+struct fuse_attr {
+    uint64_t ino;       /* inode number */
+    uint64_t size;      /* file size in bytes */
+    uint64_t blocks;    /* number of 512B blocks allocated */
+    uint64_t atime;     /* last access time (UNIX time) */
+    uint64_t mtime;     /* last modification time */
+    uint64_t ctime;     /* last status change time */
+    uint32_t atimensec; /* nanoseconds part */
+    uint32_t mtimensec;
+    uint32_t ctimensec;
+    uint32_t mode;    /* file mode (e.g. S_IFDIR | 0755) */
+    uint32_t nlink;   /* number of hard links */
+    uint32_t uid;     /* owner uid */
+    uint32_t gid;     /* owner gid */
+    uint32_t rdev;    /* device ID (if special file) */
+    uint32_t blksize; /* block size */
+    uint32_t flags;   /* reserved */
+};
+
+struct fuse_attr_out {
+    uint64_t attr_valid;      /* seconds the attributes are valid */
+    uint32_t attr_valid_nsec; /* nanoseconds part of attr_valid */
+    uint32_t dummy;           /* padding for alignment */
+    struct fuse_attr attr;    /* actual attributes */
+};
+
+struct fuse_open_in {
+    uint32_t flags;
+    uint32_t open_flags;
+};
+
+struct fuse_open_out {
+    uint64_t fh;
+    uint32_t open_flags;
+    int32_t backing_id;
+};
+
+struct fuse_read_in {
+    uint64_t fh;
+    uint64_t offset;
+    uint32_t size;
+    uint32_t read_flags;
+    uint64_t lock_owner;
+    uint32_t flags;
+    uint32_t padding;
+};
+
+struct fuse_entry_out {
+    uint64_t nodeid;           /* inode number */
+    uint64_t generation;       /* inode generation */
+    uint64_t entry_valid;      /* cache timeout (sec) */
+    uint64_t attr_valid;       /* attr cache timeout (sec) */
+    uint32_t entry_valid_nsec; /* cache timeout (nsec) */
+    uint32_t attr_valid_nsec;  /* attr cache timeout (nsec) */
+    struct fuse_attr attr;     /* file attributes */
+};
+
+struct fuse_dirent {
+    uint64_t ino;     /* inode number */
+    uint64_t off;     /* offset to next entry */
+    uint32_t namelen; /* length of the entry name */
+    uint32_t type;    /* file type (DT_REG, DT_DIR, etc.) */
+    char name[];      /* name (not null-terminated) */
+};
+
+struct fuse_direntplus {
+    struct fuse_entry_out entry_out;
+    struct fuse_dirent dirent;
+};
+
+struct fuse_lookup_in {
+    uint64_t parent; /* inode of parent dir */
+};
+
+struct fuse_forget_in {
+    uint64_t nlookup;
+};
+
+struct fuse_create_in {
+    uint32_t flags;
+    uint32_t mode;
+    uint32_t umask;
+    uint32_t open_flags;
+};
+
+struct fuse_release_in {
+    uint64_t fh;
+    uint32_t flags;
+    uint32_t release_flags;
+    uint64_t lock_owner;
+};
+
+struct fuse_flush_in {
+    uint64_t fh;
+    uint32_t unused;
+    uint32_t padding;
+    uint64_t lock_owner;
+};