fs: Add support for a filesystem

The existing filesystem support is fairly basic. It supports access to
only one filesystem at a time, does not allow caching, does not have an
equivalent of Linux's VFS and uses global variables to keep track of
which one is in use.

As a starting point to improving this, provide a filesystem uclass. For
now it only includes operations to mount and unmount.

Provide a bootdev so that it is possible to locate bootflows on a
filesystem.

Signed-off-by: Simon Glass <sjg@chromium.org>

MAINTAINERS

@@ -1182,6 +1182,12 @@ F:	net/fastboot_tcp.c
 F:	net/fastboot_udp.c
 F:	test/dm/fastboot.c
 
+FILESYSTEM LAYER
+M:	Simon Glass <sjg@chromium.org>
+S:	Maintained
+F:	fs/fs-uclass.c
+F:	include/fs.h
+
 FPGA
 M:	Michal Simek <michal.simek@amd.com>
 S:	Maintained

fs/Kconfig

@@ -4,6 +4,14 @@
 
 menu "File systems"
 
+config FS
+	bool "Support for filesystems"
+	default y if SANDBOX || VENDOR_EMULATION || ARCH_QEMU
+	depends on EXPERT
+	help
+	  Provides an interface for filesystems, allowing them to be
+	  persistently mounted. Filesystem can contain files and directory.
+
 config FS_LEGACY
 	def_bool y
 	help

fs/Makefile

@@ -5,6 +5,7 @@
 # Copyright (c) 2012, NVIDIA CORPORATION.  All rights reserved.
 
 obj-$(CONFIG_$(PHASE_)FS_LEGACY) += fs_legacy.o fs_internal.o
+obj-$(CONFIG_$(PHASE_)FS) += fs-uclass.o
 
 ifdef CONFIG_XPL_BUILD
 obj-$(CONFIG_SPL_FS_FAT) += fat/

fs/fs-uclass.c

@@ -0,0 +1,113 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Implementation of a filesystem, e.g. on a partition
+ *
+ * Copyright 2025 Simon Glass <sjg@chromium.org>
+ */
+
+#define LOG_DEBUG
+#define LOG_CATEGORY	UCLASS_FS
+
+#include <bootdev.h>
+#include <bootmeth.h>
+#include <dm.h>
+#include <fs.h>
+#include <dm/device-internal.h>
+
+int fs_mount(struct udevice *dev)
+{
+	struct fs_ops *ops = fs_get_ops(dev);
+	int ret;
+
+	ret = ops->mount(dev);
+	if (ret)
+		return log_msg_ret("fsm", ret);
+
+	ret = bootdev_setup_for_dev(dev, "fs_bootdev");
+	if (ret)
+		return log_msg_ret("fss", ret);
+
+	return 0;
+}
+
+int fs_unmount(struct udevice *dev)
+{
+	struct fs_ops *ops = fs_get_ops(dev);
+
+	return ops->unmount(dev);
+}
+
+static int fs_get_bootflow(struct udevice *dev, struct bootflow_iter *iter,
+			   struct bootflow *bflow)
+{
+	struct udevice *fsdev = dev_get_parent(dev);
+	int ret;
+
+	log_debug("get_bootflow fs '%s'\n", fsdev->name);
+
+	ret = bootmeth_check(bflow->method, iter);
+	if (ret)
+		return log_msg_ret("check", ret);
+
+	return 0;
+}
+
+static int fs_bootdev_bind(struct udevice *dev)
+{
+	struct bootdev_uc_plat *ucp = dev_get_uclass_plat(dev);
+
+	/*
+	 * we don't know what priority to give this, so pick something a little
+	 * slow for now
+	 */
+	ucp->prio = BOOTDEVP_3_INTERNAL_SLOW;
+
+	return 0;
+}
+
+static int fs_bootdev_hunt(struct bootdev_hunter *info, bool show)
+{
+	struct udevice *dev;
+	int ret;
+
+	/* mount all filesystems, which will create bootdevs for each */
+	uclass_foreach_dev_probe(UCLASS_FS, dev) {
+		ret = fs_mount(dev);
+		if (ret)
+			log_warning("Failed to mount filesystem '%s'\n",
+				    dev->name);
+	}
+
+	return 0;
+}
+
+struct bootdev_ops fs_bootdev_ops = {
+	.get_bootflow	= fs_get_bootflow,
+};
+
+static const struct udevice_id fs_bootdev_ids[] = {
+	{ .compatible = "u-boot,bootdev-fs" },
+	{ }
+};
+
+U_BOOT_DRIVER(fs_bootdev) = {
+	.name		= "fs_bootdev",
+	.id		= UCLASS_BOOTDEV,
+	.ops		= &fs_bootdev_ops,
+	.bind		= fs_bootdev_bind,
+	.of_match	= fs_bootdev_ids,
+};
+
+BOOTDEV_HUNTER(fs_bootdev_hunter) = {
+	.prio		= BOOTDEVP_3_INTERNAL_SLOW,
+	.uclass		= UCLASS_FS,
+	.hunt		= fs_bootdev_hunt,
+	.drv		= DM_DRIVER_REF(fs_bootdev),
+};
+
+UCLASS_DRIVER(fs) = {
+	.name	= "fs",
+	.id	= UCLASS_FS,
+	.per_device_auto	= sizeof(struct fs_priv),
+	.per_device_plat_auto	= sizeof(struct fs_plat),
+};

include/dm/uclass-id.h

@@ -68,6 +68,7 @@ enum uclass_id {
 	UCLASS_FIRMWARE,	/* Firmware */
 	UCLASS_FPGA,		/* FPGA device */
 	UCLASS_FUZZING_ENGINE,	/* Fuzzing engine */
+	UCLASS_FS,		/* Filesystem */
 	UCLASS_FS_FIRMWARE_LOADER,		/* Generic loader */
 	UCLASS_FWU_MDATA,	/* FWU Metadata Access */
 	UCLASS_GPIO,		/* Bank of general-purpose I/O pins */

include/fs.h

@@ -0,0 +1,78 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * U-Boot Filesystem layer
+ *
+ * Models a filesystem which can be mounted and unmounted. It also allows a
+ * directory to be looked up.
+ *
+ * Copyright 2025 Simon Glass <sjg@chromium.org>
+ */
+
+#ifndef __FS_H
+#define __FS_H
+
+#include <fs_common.h>
+
+struct udevice;
+
+enum {
+	/* Maximum length of the filesystem name */
+	FS_MAX_NAME_LEN		= 128,
+};
+
+/**
+ * struct fs_plat - Filesystem information
+ *
+ * @name: Name of the filesystem, or empty if not available
+ */
+struct fs_plat {
+	char name[FS_MAX_NAME_LEN];
+};
+
+/**
+ * struct fs_priv - Private information for the FS devices
+ *
+ * @mounted: true if mounted
+ */
+struct fs_priv {
+	bool mounted;
+};
+
+struct fs_ops {
+	/**
+	 * mount() - Mount the filesystem
+	 *
+	 * @dev: Filesystem device
+	 * Return 0 if OK, -EISCONN if already mounted, other -ve on error
+	 */
+	int (*mount)(struct udevice *dev);
+
+	/**
+	 * unmount() - Unmount the filesystem
+	 *
+	 * @dev: Filesystem device
+	 * Return 0 if OK, -ENOTCONN if not mounted, other -ve on error
+	 */
+	int (*unmount)(struct udevice *dev);
+};
+
+/* Get access to a filesystem's operations */
+#define fs_get_ops(dev)		((struct fs_ops *)(dev)->driver->ops)
+
+/**
+ * fs_mount() - Mount the filesystem
+ *
+ * @dev: Filesystem device
+ * Return 0 if OK, -EISCONN if already mounted, other -ve on error
+ */
+int fs_mount(struct udevice *dev);
+
+/**
+ * fs_unmount() - Unmount the filesystem
+ *
+ * @dev: Filesystem device
+ * Return 0 if OK, -ENOTCONN if not mounted, other -ve on error
+ */
+int fs_unmount(struct udevice *dev);
+
+#endif

test/boot/bootdev.c

@@ -390,6 +390,7 @@ static int bootdev_test_hunter(struct unit_test_state *uts)
 	ut_assert_nextlinen("----");
 	ut_assert_nextline("   6        ethernet         eth_bootdev");
 	ut_assert_nextline("   1        simple_bus       (none)");
+	ut_assert_nextline("   3        fs               fs_bootdev");
 	ut_assert_nextline("   5        ide              ide_bootdev");
 	ut_assert_nextline("   2        mmc              mmc_bootdev");
 	ut_assert_nextline("   4        nvme             nvme_bootdev");
@@ -447,6 +448,7 @@ static int bootdev_test_cmd_hunt(struct unit_test_state *uts)
 	/* This is the extension feature which has no uclass at present */
 	ut_assert_nextline("Hunting with: simple_bus");
 	ut_assert_nextline("Found 2 extension board(s).");
+	ut_assert_nextline("Hunting with: fs");
 	ut_assert_nextline("Hunting with: ide");
 
 	/* mmc hunter has already been used so should not run again */
@@ -468,6 +470,7 @@ static int bootdev_test_cmd_hunt(struct unit_test_state *uts)
 	ut_assert_nextlinen("----");
 	ut_assert_nextline("   6     *  ethernet         eth_bootdev");
 	ut_assert_nextline("   1     *  simple_bus       (none)");
+	ut_assert_nextline("   3     *  fs               fs_bootdev");
 	ut_assert_nextline("   5     *  ide              ide_bootdev");
 	ut_assert_nextline("   2     *  mmc              mmc_bootdev");
 	ut_assert_nextline("   4     *  nvme             nvme_bootdev");

test/boot/bootstd_common.h

@@ -24,10 +24,11 @@
 enum {
 	HUNTER_ETH	= 0,
 	HUNTER_SIMPLE_BUS,
-	HUNTER_MMC	= 3,
-	HUNTER_SCSI	= 6,
-	HUNTER_USB	= 8,
-	HUNTER_COUNT	= 10,
+	HUNTER_FS	= 3,
+	HUNTER_MMC,		/* ID of MMC hunter */
+	HUNTER_SCSI	= 7,	/* ID of SCSI hunter */
+	HUNTER_USB	= 9,	/* ID of USB hunter */
+	HUNTER_COUNT	= 11,
 	HUNTER_MAX	= HUNTER_COUNT - 1,
 };