U-Boot

// SPDX-License-Identifier: GPL-2.0
/*
 * U-Boot Virtio-FS Driver
 *
 * Copyright 2025 Simon Glass <sjg@chromium.org>
 *
 * This driver provides U-Boot with the ability to access a virtio-fs
 * device, allowing the bootloader to read files from a shared directory
 * on the host. This is particularly useful for loading kernels, device
 * tree blobs, and other boot-time resources.
 *
 * The driver is implemented using the U-Boot driver model and the virtio
 * uclass. It communicates with the host using the FUSE protocol over
 * virtqueues.
 */

#define LOG_CATEGORY	UCLASS_VIRTIO

#include <dir.h>
#include <dm.h>
#include <fs.h>
#include <log.h>
#include <virtio.h>
#include <virtio_fs.h>
#include <virtio_ring.h>
#include <linux/fuse.h>
#include "fs_internal.h"

#define MAX_FNAME_LEN		256	/* including \0 terminator */
#define VIRTIO_FS_TAG_SIZE	36

/**
 * struct virtio_fs_config - Configuration info for virtio-fs
 *
 * Modelled on Linux v6.15 include/uapi/linux/type.h
 *
 * @tag: filesystem name padded with NUL
 */
struct __packed virtio_fs_config {
	u8 tag[VIRTIO_FS_TAG_SIZE];
	__le32 unused1;
	__le32 unused2;
};

/*
 * Driver-private data
 *
 * @tag: Tag for the filesystem
 * @root: inode of the root node, or 0 if not known
 * @vdev: virtio device to which this FS is attached
 * @vq: Virtual queue to use
 * @config: Configuration read from QEMU
 * @root_inode: Inode of the root directory exported into QEMU
 * @next_id: ID to use for the next FUSE request
 */
struct virtio_fs_priv {
	char tag[VIRTIO_FS_TAG_SIZE + 1];
	struct virtio_device *vdev;
	struct virtqueue *vq;
	struct virtio_fs_config config;
	u64 root_inode;
	int next_id;
};

u64 virtio_fs_get_root(struct udevice *dev)
{
	struct virtio_fs_priv *priv = dev_get_priv(dev);

	return priv->root_inode;
}

/**
 * virtio_fs_xfer() - Perform a transfer of a FUSE request
 *
 * @dev: virtio-fs device to use (UCLASS_FS)
 * @inhdr: FUSE header to send
 * @in: Extra data to send (must be present)
 * @insize: Size of data to send
 * @outhdr: Returns the output header received via FUSE
 * @out: Place to put extra output data (NULL if none)
 * @outsize: Size of output buffer at @out (must be 0 if @out is NULL)
 * Return: 0 if OK, -ve on error
 */
static int virtio_fs_xfer(struct udevice *dev, struct fuse_in_header *inhdr,
			  const void *in, int insize,
			  struct fuse_out_header *outhdr, void *out,
			  int outsize)
{
	struct virtio_fs_priv *priv = dev_get_priv(dev);
	struct virtqueue *vq = priv->vq;
	struct virtio_sg sg[4];
	struct virtio_sg *sgs[4];
	uint dummy_len;
	int i, ret;

	inhdr->unique = priv->next_id++;

	sg[0].addr = inhdr;
	sg[0].length = sizeof(*inhdr);
	sg[1].addr = (void *)in;
	sg[1].length = insize;
	sg[2].addr = outhdr;
	sg[2].length = sizeof(*outhdr);
	sg[3].addr = out;
	sg[3].length = outsize;
	for (i = 0; i < 4; i++)
		sgs[i] = &sg[i];
	inhdr->len = sizeof(*inhdr) + insize;
	outhdr->len = sizeof(*outhdr) + outsize;

	log_debug("sg[1].addr %p sg[3].length %zx\n", sg[1].addr, sg[3].length);
	ret = virtqueue_add(vq, sgs, 2, out ? 2 : 1);
	if (ret) {
		log_err("Failed to add buffers to virtqueue\n");
		return ret;
	}

	virtqueue_kick(vq);

	log_debug("wait...");
	while (!virtqueue_get_buf(vq, &dummy_len))
		;
	log_debug("done\n");
	if (outhdr->error)
		return log_msg_ret("vix", outhdr->error);

	return 0;
}

int virtio_fs_lookup_(struct udevice *dev, u64 nodeid, const char *name,
		      struct fuse_entry_out *out)
{
	struct fuse_in_header inhdr = {};
	struct fuse_out_header outhdr;
	int name_len = strlen(name) + 1;
	int ret;

	inhdr.opcode = FUSE_LOOKUP;
	inhdr.nodeid = nodeid;

	ret = virtio_fs_xfer(dev, &inhdr, name, name_len, &outhdr, out,
			     sizeof(struct fuse_entry_out));
	log_debug("len %x error %x unique %llx\n", outhdr.len, outhdr.error,
		  outhdr.unique);
	if (ret)
		return log_msg_ret("vfl", ret);

	return 0;
}

int virtio_fs_lookup(struct udevice *dev, const char *name, u64 *entryp)
{
	struct virtio_fs_priv *priv = dev_get_priv(dev);
	struct fuse_entry_out out;
	int ret;

	log_debug("dev '%s': lookup in inode %llx name '%s'\n", dev->name,
		  priv->root_inode, name);
	ret = virtio_fs_lookup_(dev, priv->root_inode, name, &out);
	if (ret)
		return log_msg_ret("vfl", ret);
	*entryp = out.nodeid;

	return 0;
}

int virtio_fs_forget(struct udevice *dev, u64 nodeid)
{
	struct fuse_in_header inhdr = {};
	struct fuse_forget_in in;
	struct fuse_out_header outhdr;
	int ret;

	inhdr.opcode = FUSE_FORGET;
	inhdr.nodeid = nodeid;
	in.nlookup = 1;

	ret = virtio_fs_xfer(dev, &inhdr, &in, sizeof(in), &outhdr, NULL, 0);
	log_debug("len %x error %x unique %llx\n", outhdr.len, outhdr.error,
		  outhdr.unique);
	if (ret)
		return log_msg_ret("vfl", ret);

	return 0;
}

int virtio_fs_opendir(struct udevice *dev, u64 nodeid, u64 *fhp)
{
	struct fuse_in_header inhdr = {};
	struct fuse_open_in in = {};
	struct fuse_out_header outhdr;
	struct fuse_open_out out;
	int ret;

	inhdr.opcode = FUSE_OPENDIR;
	inhdr.nodeid = nodeid;

	ret = virtio_fs_xfer(dev, &inhdr, &in, sizeof(in), &outhdr, &out,
			     sizeof(struct fuse_open_out));
	log_debug("fh %llx open_flags %x backing_id %x\n", out.fh,
		  out.open_flags, out.backing_id);
	log_debug("len %x error %x unique %llx\n", outhdr.len, outhdr.error,
		  outhdr.unique);
	if (ret)
		return log_msg_ret("vfo", ret);
	*fhp = out.fh;

	return 0;
}

int virtio_fs_readdir(struct udevice *dev, u64 nodeid, u64 fh, u64 offset,
		      void *buf, int size, int *out_sizep)
{
	struct fuse_in_header inhdr = {};
	struct fuse_read_in in = {};
	struct fuse_out_header outhdr;
	uint len;
	int ret;

	inhdr.opcode = FUSE_READDIRPLUS;
	inhdr.nodeid = nodeid;

	in.fh = fh;
	in.size = size;
	in.offset = offset;
	ret = virtio_fs_xfer(dev, &inhdr, &in, sizeof(in), &outhdr, buf, size);
	log_debug("fh %llx offset %llx\n", in.fh, in.offset);
	log_debug("len %x error %x unique %llx\n", outhdr.len, outhdr.error,
		  outhdr.unique);
	if (ret)
		return log_msg_ret("vfr", ret);

	len = outhdr.len - sizeof(outhdr);
	/* sanity check */
	if (len > size) {
		log_debug("virtio: internal size error outhdr.len %x size %x\n",
			  outhdr.len, size);
		return log_msg_ret("vle", -EFAULT);
	}
	*out_sizep = len;

	return 0;
}

int virtio_fs_releasedir(struct udevice *dev, u64 nodeid, u64 fh)
{
	struct fuse_in_header inhdr = {};
	struct fuse_release_in in = {};
	struct fuse_out_header outhdr;
	int ret;

	inhdr.opcode = FUSE_RELEASEDIR;
	inhdr.nodeid = nodeid;
	in.fh = fh;

	ret = virtio_fs_xfer(dev, &inhdr, &in, sizeof(in), &outhdr, NULL, 0);
	if (ret)
		return log_msg_ret("vfe", ret);
	log_debug("len %x error %x unique %llx\n", outhdr.len, outhdr.error,
		  outhdr.unique);

	return 0;
}

int virtio_fs_open_file(struct udevice *dev, u64 nodeid,
			enum dir_open_flags_t flags, u64 *fhp, uint *flagsp)
{
	struct fuse_in_header inhdr = {};
	char buf[MAX_FNAME_LEN + sizeof(struct fuse_open_in)];
	struct fuse_open_in *in = (struct fuse_open_in *)buf;
	struct fuse_out_header outhdr;
	struct fuse_open_out out;
	int ret;

	inhdr.opcode = FUSE_OPEN;
	inhdr.nodeid = nodeid;

	in->flags = 0;
	in->open_flags = flags;

	ret = virtio_fs_xfer(dev, &inhdr, buf, sizeof(*in), &outhdr,
			     &out, sizeof(struct fuse_open_out));
	if (ret)
		return log_msg_ret("vfr", ret);

	*fhp = out.fh;
	*flagsp = out.open_flags;

	return 0;
}

long virtio_fs_read(struct udevice *dev, u64 nodeid, u64 fh, u64 offset,
		    void *buf, uint size)
{
	struct fuse_in_header inhdr = {};
	struct fuse_read_in in = {};
	struct fuse_out_header outhdr;
	int ret;

	log_debug("dev '%s' nodeid %lld fh %lld offset %llx size %x buf %p\n",
		  dev->name, nodeid, fh, offset, size, buf);
	inhdr.opcode = FUSE_READ;
	inhdr.nodeid = nodeid;

	in.fh = fh;
	in.offset = offset;
	in.size = size;

	ret = virtio_fs_xfer(dev, &inhdr, &in, sizeof(in), &outhdr, buf, size);
	if (ret)
		return log_msg_ret("vfr", ret);
	log_debug("read len %x\n", outhdr.len);

	return outhdr.len;
}

static int virtio_fs_init(struct udevice *dev)
{
	struct fuse_in_header inhdr = {};
	struct fuse_init_in in = {};
	struct fuse_out_header outhdr;
	struct fuse_init_out out;
	int ret;

	inhdr.opcode = FUSE_INIT;

	in.major = FUSE_KERNEL_VERSION;
	in.minor = FUSE_KERNEL_MINOR_VERSION;

	ret = virtio_fs_xfer(dev, &inhdr, &in, sizeof(in), &outhdr, &out,
			     sizeof(out));
	if (ret)
		return log_msg_ret("vfx", ret);
	log_debug("major %x minor %x max_readahead %x flags %x ", out.major,
		  out.minor, out.max_readahead, out.flags);
	log_debug("max_background %x congestion_threshold %x max_write %x\n",
		  out.max_background, out.congestion_threshold, out.max_write);
	log_debug("time_gran %x max_pages %x, map_alignment %x flags2 %x ",
		  out.time_gran, out.max_pages, out.map_alignment, out.flags2);
	log_debug("max_stack_depth %x request_timeout %x\n",
		  out.max_stack_depth, out.request_timeout);

	return 0;
}

static int _virtio_fs_probe(struct udevice *dev)
{
	struct virtio_dev_priv *virtio_priv = dev_get_uclass_priv(dev->parent);
	struct virtio_fs_priv *priv = dev_get_priv(dev);
	int ret;

	/* Indicate what driver features we support */
	virtio_driver_features_init(virtio_priv, NULL, 0, NULL, 0);

	virtio_cread_bytes(dev, 0, &priv->tag, VIRTIO_FS_TAG_SIZE);
	priv->tag[VIRTIO_FS_TAG_SIZE] = '\0';

	log_debug("tag %s\n", priv->tag);

	ret = virtio_find_vqs(dev, 1, &priv->vq);
	if (ret)
		return log_msg_ret("vff", ret);

	return 0;
}

static int virtio_fs_mount(struct udevice *dev)
{
	struct fs_priv *uc_priv = dev_get_uclass_priv(dev);
	struct virtio_fs_priv *priv = dev_get_priv(dev);
	struct fuse_entry_out out;
	int ret;

	if (uc_priv->mounted)
		return log_msg_ret("vfi", -EISCONN);
	if (IS_ENABLED(CONFIG_SANDBOX))
		return log_msg_ret("vfs", -ENOENT);

	ret = virtio_fs_init(dev);
	if (ret)
		return log_msg_ret("vfi", ret);

	ret = virtio_fs_lookup_(dev, FUSE_ROOT_ID, ".", &out);
	if (ret) {
		log_err("Failed to lookup root directory: %d\n", ret);
		return ret;
	}
	priv->root_inode = out.nodeid;
	log_debug("directory found, ino=%lld\n", priv->root_inode);

	uc_priv->mounted = true;

	return 0;
}

static int virtio_fs_unmount(struct udevice *dev)
{
	struct fs_priv *uc_priv = dev_get_uclass_priv(dev);
	struct virtio_fs_priv *priv = dev_get_priv(dev);
	int ret;

	if (!uc_priv->mounted)
		return log_msg_ret("vfu", -ENOTCONN);

	ret = virtio_fs_forget(dev, priv->root_inode);
	if (ret)
		return log_msg_ret("vff", ret);

	return 0;
}

static const struct fs_ops virtio_fs_ops = {
	.mount		= virtio_fs_mount,
	.unmount	= virtio_fs_unmount,
	.lookup_dir	= virtio_fs_setup_dir,
};

static const struct udevice_id virtio_fs_ids[] = {
	{ .compatible = "virtio,fs" },
	{ }
};

U_BOOT_DRIVER(virtio_fs) = {
	.name	= VIRTIO_FS_DRV_NAME,
	.id	= UCLASS_FS,
	.of_match = virtio_fs_ids,
	.ops	= &virtio_fs_ops,
	.probe	= _virtio_fs_probe,
	.priv_auto	= sizeof(struct virtio_fs_priv),
	.flags	= DM_FLAG_ACTIVE_DMA,
};