[PATCH 2/4] fs: 9p: Add 9P filesystem support
Kuan-Wei Chiu
visitorckw at gmail.com
Mon Jul 6 23:54:44 CEST 2026
Implement the VFS interface for the 9P filesystem.
Map the U-Boot filesystem operations to the underlying 9P protocol
client. It also registers the 9P filesystem type within the U-Boot
generic fs framework, allowing it to bypass standard block device
partition checks since 9P is a network/host-backed filesystem.
Signed-off-by: Kuan-Wei Chiu <visitorckw at gmail.com>
---
fs/9p/9p.c | 137 +++++++++++++++++++++++++++++++++++++++++++++++++
fs/9p/Kconfig | 8 +++
fs/9p/Makefile | 5 ++
fs/Kconfig | 2 +
fs/Makefile | 1 +
fs/fs.c | 35 +++++++++++++
include/fs.h | 1 +
7 files changed, 189 insertions(+)
create mode 100644 fs/9p/9p.c
create mode 100644 fs/9p/Kconfig
create mode 100644 fs/9p/Makefile
diff --git a/fs/9p/9p.c b/fs/9p/9p.c
new file mode 100644
index 00000000000..37d60c03891
--- /dev/null
+++ b/fs/9p/9p.c
@@ -0,0 +1,137 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2026, Kuan-Wei Chiu <visitorckw at gmail.com>
+ */
+
+#include <9p.h>
+#include <config.h>
+#include <log.h>
+#include <asm/unaligned.h>
+#include <linux/errno.h>
+#include <linux/string.h>
+#include <linux/types.h>
+
+static u32 p9_root_fid = 1;
+
+int p9_fs_probe(struct blk_desc *fs_dev_desc, struct disk_partition *fs_partition)
+{
+ struct p9_client *c = p9_get_client();
+
+ if (!c) {
+ log_err("9P Error: No transport client registered\n");
+ return -ENODEV;
+ }
+
+ if (p9_client_version(c))
+ return -EIO;
+ if (p9_client_attach(c, p9_root_fid, "root", ""))
+ return -EIO;
+
+ return 0;
+}
+
+int p9_fs_ls(const char *dirname)
+{
+ struct p9_client *c = p9_get_client();
+ u32 fid = p9_client_alloc_fid(c);
+ u8 buf[4096];
+ u32 actread;
+ u8 *ptr, *end;
+ u16 name_len;
+ u8 d_type;
+
+ if (p9_client_walk(c, p9_root_fid, fid, dirname))
+ return -ENOENT;
+ if (p9_client_lopen(c, fid, P9_O_RDONLY))
+ return -EIO;
+
+ if (p9_client_readdir(c, fid, 0, sizeof(buf), buf, &actread)) {
+ p9_client_clunk(c, fid);
+ return -EIO;
+ }
+
+ if (actread == 0) {
+ printf(" (empty directory)\n");
+ } else {
+ ptr = buf;
+ end = buf + actread;
+ while (ptr < end) {
+ ptr += P9_DIRENT_OFFSET;
+ d_type = *ptr++;
+ name_len = get_unaligned_le16(ptr);
+ ptr += 2;
+ printf(" %s %.*s\n", (d_type == P9_DT_DIR) ? "<DIR> " : " ",
+ name_len, ptr);
+ ptr += name_len;
+ }
+ }
+
+ p9_client_clunk(c, fid);
+ return 0;
+}
+
+int p9_fs_size(const char *filename, loff_t *size)
+{
+ struct p9_client *c = p9_get_client();
+ u32 fid = p9_client_alloc_fid(c);
+ int ret;
+
+ if (p9_client_walk(c, p9_root_fid, fid, filename))
+ return -ENOENT;
+ ret = p9_client_stat(c, fid, size);
+ p9_client_clunk(c, fid);
+
+ return ret;
+}
+
+int p9_fs_exists(const char *filename)
+{
+ loff_t size;
+
+ return (p9_fs_size(filename, &size) == 0) ? 1 : 0;
+}
+
+int p9_fs_read(const char *filename, void *buf, loff_t offset, loff_t len, loff_t *actread)
+{
+ struct p9_client *c = p9_get_client();
+ u32 fid = p9_client_alloc_fid(c);
+ u32 read_bytes = 0;
+ loff_t total_read = 0;
+ loff_t remaining;
+ u32 req_len;
+ u8 *dst = (u8 *)buf;
+ int ret = 0;
+
+ if (p9_client_walk(c, p9_root_fid, fid, filename))
+ return -ENOENT;
+ if (p9_client_lopen(c, fid, P9_O_RDONLY)) {
+ p9_client_clunk(c, fid);
+ return -EIO;
+ }
+
+ while (1) {
+ if (len == 0) {
+ req_len = 0;
+ } else {
+ remaining = len - total_read;
+ if (remaining == 0)
+ break;
+
+ req_len = (remaining > 0xFFFFFFFF) ? 0xFFFFFFFF : (u32)remaining;
+ }
+
+ ret = p9_client_read(c, fid, offset, req_len, dst, &read_bytes);
+
+ if (ret != 0 || read_bytes == 0)
+ break;
+
+ total_read += read_bytes;
+ offset += read_bytes;
+ dst += read_bytes;
+ }
+
+ *actread = total_read;
+ p9_client_clunk(c, fid);
+
+ return (total_read > 0 || ret == 0) ? 0 : ret;
+}
diff --git a/fs/9p/Kconfig b/fs/9p/Kconfig
new file mode 100644
index 00000000000..bc6d4962288
--- /dev/null
+++ b/fs/9p/Kconfig
@@ -0,0 +1,8 @@
+config FS_9P
+ bool "9P filesystem support"
+ depends on NET_9P
+ help
+ This provides support for the 9P2000.L filesystem.
+
+ To use this filesystem, you also need to enable a 9P
+ transport driver.
diff --git a/fs/9p/Makefile b/fs/9p/Makefile
new file mode 100644
index 00000000000..c7f7553e8f4
--- /dev/null
+++ b/fs/9p/Makefile
@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+#
+# Copyright (C) 2026, Kuan-Wei Chiu <visitorckw at gmail.com>
+
+obj-y += 9p.o
diff --git a/fs/Kconfig b/fs/Kconfig
index e0b0b901e1d..e4aa726ea35 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -26,4 +26,6 @@ source "fs/squashfs/Kconfig"
source "fs/erofs/Kconfig"
+source "fs/9p/Kconfig"
+
endmenu
diff --git a/fs/Makefile b/fs/Makefile
index ce5e74257a0..5aa34b39172 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -26,5 +26,6 @@ obj-$(CONFIG_CMD_UBIFS) += ubifs/
obj-$(CONFIG_CMD_ZFS) += zfs/
obj-$(CONFIG_FS_SQUASHFS) += squashfs/
obj-$(CONFIG_FS_EROFS) += erofs/
+obj-$(CONFIG_FS_9P) += 9p/
endif
obj-y += fs_internal.o
diff --git a/fs/fs.c b/fs/fs.c
index 8ea50a6c13c..0bb996dede5 100644
--- a/fs/fs.c
+++ b/fs/fs.c
@@ -32,6 +32,7 @@
#include <squashfs.h>
#include <erofs.h>
#include <exfat.h>
+#include <9p.h>
static struct blk_desc *fs_dev_desc;
static int fs_dev_part;
@@ -398,6 +399,26 @@ static struct fstype_info fstypes[] = {
.mkdir = exfat_fs_mkdir,
.rename = exfat_fs_rename,
},
+#endif
+#if CONFIG_IS_ENABLED(FS_9P)
+ {
+ .fstype = FS_TYPE_9P,
+ .name = "9p",
+ .null_dev_desc_ok = true,
+ .probe = p9_fs_probe,
+ .close = fs_close_unsupported,
+ .ls = p9_fs_ls,
+ .exists = p9_fs_exists,
+ .size = p9_fs_size,
+ .read = p9_fs_read,
+ .write = fs_write_unsupported,
+ .uuid = fs_uuid_unsupported,
+ .opendir = fs_opendir_unsupported,
+ .unlink = fs_unlink_unsupported,
+ .mkdir = fs_mkdir_unsupported,
+ .ln = fs_ln_unsupported,
+ .rename = fs_rename_unsupported,
+ },
#endif
{
.fstype = FS_TYPE_ANY,
@@ -464,6 +485,20 @@ int fs_set_blk_dev(const char *ifname, const char *dev_part_str, int fstype)
struct fstype_info *info;
int part, i;
+ /* Intercept 9p to bypass block device partition checks */
+ if (CONFIG_IS_ENABLED(FS_9P) && !strncmp(ifname, "9p", 2)) {
+ for (i = 0, info = fstypes; i < ARRAY_SIZE(fstypes); i++, info++) {
+ if (info->fstype == FS_TYPE_9P) {
+ fs_dev_desc = NULL;
+ fs_type = FS_TYPE_9P;
+ if (info->probe(fs_dev_desc, NULL))
+ return -1;
+ return 0;
+ }
+ }
+ return -1;
+ }
+
part = part_get_info_by_dev_and_name_or_num(ifname, dev_part_str, &fs_dev_desc,
&fs_partition, 1);
if (part < 0)
diff --git a/include/fs.h b/include/fs.h
index bec02117737..8afc81c0017 100644
--- a/include/fs.h
+++ b/include/fs.h
@@ -19,6 +19,7 @@ struct cmd_tbl;
#define FS_TYPE_EROFS 7
#define FS_TYPE_SEMIHOSTING 8
#define FS_TYPE_EXFAT 9
+#define FS_TYPE_9P 10
struct blk_desc;
--
2.55.0.rc2.803.g1fd1e6609c-goog
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