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debugfs: Remove broken no-mount mode

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debugfs access modes were added in Linux 5.10 (Dec 2020) [1], but the
no-mount mode has behaved effectively the same as the off mode since
Linux 5.12 (Apr 2021) [2]. The only difference is the specific error
code returned by the debugfs_create_* functions, which is -ENOENT in
no-mount mode and -EPERM in off mode.

Given that no-mount hasn't worked for several years with no complaints,
just remove it.

[1] a24c6f7bc9 ("debugfs: Add access restriction option")

[2] bc6de804d3 ("debugfs: be more robust at handling improper input in debugfs_lookup()")
    56348560d4 ("debugfs: do not attempt to create a new file before the filesystem is initalized")

Signed-off-by: Aaron Thompson <dev@aaront.org>
Link: https://patch.msgid.link/20251120102222.18371-3-dev@null.aaront.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Aaron Thompson
2025-11-20 10:26:33 +00:00
committed by Greg Kroah-Hartman
parent 3ae94a55d0
commit f278809475
4 changed files with 13 additions and 33 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
Documentation/admin-guide/kernel-parameters.txt
View File

@@ -1113,12 +1113,8 @@
debugfs= [KNL,EARLY] This parameter enables what is exposed to
userspace and debugfs internal clients.
Format: { on, no-mount, off }
Format: { on, off }
on: All functions are enabled.
no-mount:
Filesystem is not registered but kernel clients can
access APIs and a crashkernel can be used to read
its content. There is nothing to mount.
off: Filesystem is not registered and clients
get a -EPERM as result when trying to register files
or directories within debugfs.

18
fs/debugfs/inode.c
View File

@@ -35,7 +35,7 @@
static struct vfsmount *debugfs_mount;
static int debugfs_mount_count;
static bool debugfs_registered;
static unsigned int debugfs_allow __ro_after_init = DEFAULT_DEBUGFS_ALLOW_BITS;
static bool debugfs_enabled __ro_after_init = IS_ENABLED(DEBUG_FS_ALLOW_ALL);
/*
* Don't allow access attributes to be changed whilst the kernel is locked down
@@ -365,7 +365,7 @@ static struct dentry *debugfs_start_creating(const char *name,
struct dentry *dentry;
int error;
if (!(debugfs_allow & DEBUGFS_ALLOW_API))
if (!debugfs_enabled)
return ERR_PTR(-EPERM);
if (!debugfs_initialized())
@@ -885,21 +885,25 @@ static int __init debugfs_kernel(char *str)
{
if (str) {
if (!strcmp(str, "on"))
debugfs_allow = DEBUGFS_ALLOW_API | DEBUGFS_ALLOW_MOUNT;
else if (!strcmp(str, "no-mount"))
debugfs_allow = DEBUGFS_ALLOW_API;
debugfs_enabled = true;
else if (!strcmp(str, "off"))
debugfs_allow = 0;
debugfs_enabled = false;
else if (!strcmp(str, "no-mount")) {
pr_notice("debugfs=no-mount is a deprecated alias "
"for debugfs=off\n");
debugfs_enabled = false;
}
}
return 0;
}
early_param("debugfs", debugfs_kernel);
static int __init debugfs_init(void)
{
int retval;
if (!(debugfs_allow & DEBUGFS_ALLOW_MOUNT))
if (!debugfs_enabled)
return -EPERM;
retval = sysfs_create_mount_point(kernel_kobj, "debug");

13
fs/debugfs/internal.h
View File

@@ -55,17 +55,4 @@ enum {
HAS_IOCTL = 16
};
#define DEBUGFS_ALLOW_API BIT(0)
#define DEBUGFS_ALLOW_MOUNT BIT(1)
#ifdef CONFIG_DEBUG_FS_ALLOW_ALL
#define DEFAULT_DEBUGFS_ALLOW_BITS (DEBUGFS_ALLOW_MOUNT | DEBUGFS_ALLOW_API)
#endif
#ifdef CONFIG_DEBUG_FS_DISALLOW_MOUNT
#define DEFAULT_DEBUGFS_ALLOW_BITS (DEBUGFS_ALLOW_API)
#endif
#ifdef CONFIG_DEBUG_FS_ALLOW_NONE
#define DEFAULT_DEBUGFS_ALLOW_BITS (0)
#endif
#endif /* _DEBUGFS_INTERNAL_H_ */

9
lib/Kconfig.debug
View File

@@ -679,7 +679,7 @@ choice
help
This selects the default access restrictions for debugfs.
It can be overridden with kernel command line option
debugfs=[on,no-mount,off]. The restrictions apply for API access
debugfs=[on,off]. The restrictions apply for API access
and filesystem registration.
config DEBUG_FS_ALLOW_ALL
@@ -688,13 +688,6 @@ config DEBUG_FS_ALLOW_ALL
No restrictions apply. Both API and filesystem registration
is on. This is the normal default operation.
config DEBUG_FS_DISALLOW_MOUNT
bool "Do not register debugfs as filesystem"
help
The API is open but filesystem is not loaded. Clients can still do
their work and read with debug tools that do not need
debugfs filesystem.
config DEBUG_FS_ALLOW_NONE
bool "No access"
help