[PATCH bpf-next 0/2] umd: Remove usermode driver framework

[PATCH bpf-next 0/2] umd: Remove usermode driver framework

[Thomas Weißschuh]

The code is unused, remove it.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
---
Thomas Weißschuh (2):
      bpf/preload: Don't select USERMODE_DRIVER
      umd: Remove usermode driver framework

 include/linux/usermode_driver.h |  19 ----
 kernel/Makefile                 |   1 -
 kernel/bpf/preload/Kconfig      |   5 --
 kernel/usermode_driver.c        | 191 ----------------------------------------
 4 files changed, 216 deletions(-)
---
base-commit: 19272b37aa4f83ca52bdf9c16d5d81bdd1354494
change-id: 20250721-remove-usermode-driver-aecfe2950c59

Best regards,
-- 
Thomas Weißschuh <thomas.weissschuh@linutronix.de>

[PATCH bpf-next 1/2] bpf/preload: Don't select USERMODE_DRIVER

[Thomas Weißschuh]

The usermode driver framework is not used anymore by the BPF preload code.

Fixes: cb80ddc67152 ("bpf: Convert bpf_preload.ko to use light skeleton.")
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
---
 kernel/bpf/preload/Kconfig | 1 -
 1 file changed, 1 deletion(-)

diff --git a/kernel/bpf/preload/Kconfig b/kernel/bpf/preload/Kconfig
index c9d45c9d6918d1402dab634e280b56c5c929a858..f9b11d01c3b50d4e98a33c686b55015766d17902 100644
--- a/kernel/bpf/preload/Kconfig
+++ b/kernel/bpf/preload/Kconfig
@@ -10,7 +10,6 @@ menuconfig BPF_PRELOAD
 	# The dependency on !COMPILE_TEST prevents it from being enabled
 	# in allmodconfig or allyesconfig configurations
 	depends on !COMPILE_TEST
-	select USERMODE_DRIVER
 	help
 	  This builds kernel module with several embedded BPF programs that are
 	  pinned into BPF FS mount point as human readable files that are

-- 
2.50.1

Re: [PATCH bpf-next 1/2] bpf/preload: Don't select USERMODE_DRIVER

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

[PATCH bpf-next 2/2] umd: Remove usermode driver framework

[Thomas Weißschuh]

The code is unused since commit 98e20e5e13d2 ("bpfilter: remove bpfilter"),
remove it.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
---
 include/linux/usermode_driver.h |  19 ----
 kernel/Makefile                 |   1 -
 kernel/bpf/preload/Kconfig      |   4 -
 kernel/usermode_driver.c        | 191 ----------------------------------------
 4 files changed, 215 deletions(-)

diff --git a/include/linux/usermode_driver.h b/include/linux/usermode_driver.h
deleted file mode 100644
index ad970416260dd208b43098e17df9ad49b4da7693..0000000000000000000000000000000000000000
--- a/include/linux/usermode_driver.h
+++ /dev/null
@@ -1,19 +0,0 @@
-#ifndef __LINUX_USERMODE_DRIVER_H__
-#define __LINUX_USERMODE_DRIVER_H__
-
-#include <linux/umh.h>
-#include <linux/path.h>
-
-struct umd_info {
-	const char *driver_name;
-	struct file *pipe_to_umh;
-	struct file *pipe_from_umh;
-	struct path wd;
-	struct pid *tgid;
-};
-int umd_load_blob(struct umd_info *info, const void *data, size_t len);
-int umd_unload_blob(struct umd_info *info);
-int fork_usermode_driver(struct umd_info *info);
-void umd_cleanup_helper(struct umd_info *info);
-
-#endif /* __LINUX_USERMODE_DRIVER_H__ */
diff --git a/kernel/Makefile b/kernel/Makefile
index 32e80dd626af07d0c43290e3f5c64af5bff07b51..4332de7ffdee40f6a1cf77ff4b422b51142838e9 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -12,7 +12,6 @@ obj-y     = fork.o exec_domain.o panic.o \
 	    notifier.o ksysfs.o cred.o reboot.o \
 	    async.o range.o smpboot.o ucount.o regset.o ksyms_common.o
 
-obj-$(CONFIG_USERMODE_DRIVER) += usermode_driver.o
 obj-$(CONFIG_MULTIUSER) += groups.o
 obj-$(CONFIG_VHOST_TASK) += vhost_task.o
 
diff --git a/kernel/bpf/preload/Kconfig b/kernel/bpf/preload/Kconfig
index f9b11d01c3b50d4e98a33c686b55015766d17902..aef7b0bc96d6113dbca7ab4b9510c3dcf39a97f4 100644
--- a/kernel/bpf/preload/Kconfig
+++ b/kernel/bpf/preload/Kconfig
@@ -1,8 +1,4 @@
 # SPDX-License-Identifier: GPL-2.0-only
-config USERMODE_DRIVER
-	bool
-	default n
-
 menuconfig BPF_PRELOAD
 	bool "Preload BPF file system with kernel specific program and map iterators"
 	depends on BPF
diff --git a/kernel/usermode_driver.c b/kernel/usermode_driver.c
deleted file mode 100644
index 8303f4c7ca714a0aa96aeec4be8c8423ce8a200d..0000000000000000000000000000000000000000
--- a/kernel/usermode_driver.c
+++ /dev/null
@@ -1,191 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0-only
-/*
- * umd - User mode driver support
- */
-#include <linux/shmem_fs.h>
-#include <linux/pipe_fs_i.h>
-#include <linux/mount.h>
-#include <linux/fs_struct.h>
-#include <linux/task_work.h>
-#include <linux/usermode_driver.h>
-
-static struct vfsmount *blob_to_mnt(const void *data, size_t len, const char *name)
-{
-	struct file_system_type *type;
-	struct vfsmount *mnt;
-	struct file *file;
-	ssize_t written;
-	loff_t pos = 0;
-
-	type = get_fs_type("tmpfs");
-	if (!type)
-		return ERR_PTR(-ENODEV);
-
-	mnt = kern_mount(type);
-	put_filesystem(type);
-	if (IS_ERR(mnt))
-		return mnt;
-
-	file = file_open_root_mnt(mnt, name, O_CREAT | O_WRONLY, 0700);
-	if (IS_ERR(file)) {
-		kern_unmount(mnt);
-		return ERR_CAST(file);
-	}
-
-	written = kernel_write(file, data, len, &pos);
-	if (written != len) {
-		int err = written;
-		if (err >= 0)
-			err = -ENOMEM;
-		filp_close(file, NULL);
-		kern_unmount(mnt);
-		return ERR_PTR(err);
-	}
-
-	fput(file);
-
-	/* Flush delayed fput so exec can open the file read-only */
-	flush_delayed_fput();
-	task_work_run();
-	return mnt;
-}
-
-/**
- * umd_load_blob - Remember a blob of bytes for fork_usermode_driver
- * @info: information about usermode driver
- * @data: a blob of bytes that can be executed as a file
- * @len:  The lentgh of the blob
- *
- */
-int umd_load_blob(struct umd_info *info, const void *data, size_t len)
-{
-	struct vfsmount *mnt;
-
-	if (WARN_ON_ONCE(info->wd.dentry || info->wd.mnt))
-		return -EBUSY;
-
-	mnt = blob_to_mnt(data, len, info->driver_name);
-	if (IS_ERR(mnt))
-		return PTR_ERR(mnt);
-
-	info->wd.mnt = mnt;
-	info->wd.dentry = mnt->mnt_root;
-	return 0;
-}
-EXPORT_SYMBOL_GPL(umd_load_blob);
-
-/**
- * umd_unload_blob - Disassociate @info from a previously loaded blob
- * @info: information about usermode driver
- *
- */
-int umd_unload_blob(struct umd_info *info)
-{
-	if (WARN_ON_ONCE(!info->wd.mnt ||
-			 !info->wd.dentry ||
-			 info->wd.mnt->mnt_root != info->wd.dentry))
-		return -EINVAL;
-
-	kern_unmount(info->wd.mnt);
-	info->wd.mnt = NULL;
-	info->wd.dentry = NULL;
-	return 0;
-}
-EXPORT_SYMBOL_GPL(umd_unload_blob);
-
-static int umd_setup(struct subprocess_info *info, struct cred *new)
-{
-	struct umd_info *umd_info = info->data;
-	struct file *from_umh[2];
-	struct file *to_umh[2];
-	int err;
-
-	/* create pipe to send data to umh */
-	err = create_pipe_files(to_umh, 0);
-	if (err)
-		return err;
-	err = replace_fd(0, to_umh[0], 0);
-	fput(to_umh[0]);
-	if (err < 0) {
-		fput(to_umh[1]);
-		return err;
-	}
-
-	/* create pipe to receive data from umh */
-	err = create_pipe_files(from_umh, 0);
-	if (err) {
-		fput(to_umh[1]);
-		replace_fd(0, NULL, 0);
-		return err;
-	}
-	err = replace_fd(1, from_umh[1], 0);
-	fput(from_umh[1]);
-	if (err < 0) {
-		fput(to_umh[1]);
-		replace_fd(0, NULL, 0);
-		fput(from_umh[0]);
-		return err;
-	}
-
-	set_fs_pwd(current->fs, &umd_info->wd);
-	umd_info->pipe_to_umh = to_umh[1];
-	umd_info->pipe_from_umh = from_umh[0];
-	umd_info->tgid = get_pid(task_tgid(current));
-	return 0;
-}
-
-static void umd_cleanup(struct subprocess_info *info)
-{
-	struct umd_info *umd_info = info->data;
-
-	/* cleanup if umh_setup() was successful but exec failed */
-	if (info->retval)
-		umd_cleanup_helper(umd_info);
-}
-
-/**
- * umd_cleanup_helper - release the resources which were allocated in umd_setup
- * @info: information about usermode driver
- */
-void umd_cleanup_helper(struct umd_info *info)
-{
-	fput(info->pipe_to_umh);
-	fput(info->pipe_from_umh);
-	put_pid(info->tgid);
-	info->tgid = NULL;
-}
-EXPORT_SYMBOL_GPL(umd_cleanup_helper);
-
-/**
- * fork_usermode_driver - fork a usermode driver
- * @info: information about usermode driver (shouldn't be NULL)
- *
- * Returns either negative error or zero which indicates success in
- * executing a usermode driver. In such case 'struct umd_info *info'
- * is populated with two pipes and a tgid of the process. The caller is
- * responsible for health check of the user process, killing it via
- * tgid, and closing the pipes when user process is no longer needed.
- */
-int fork_usermode_driver(struct umd_info *info)
-{
-	struct subprocess_info *sub_info;
-	const char *argv[] = { info->driver_name, NULL };
-	int err;
-
-	if (WARN_ON_ONCE(info->tgid))
-		return -EBUSY;
-
-	err = -ENOMEM;
-	sub_info = call_usermodehelper_setup(info->driver_name,
-					     (char **)argv, NULL, GFP_KERNEL,
-					     umd_setup, umd_cleanup, info);
-	if (!sub_info)
-		goto out;
-
-	err = call_usermodehelper_exec(sub_info, UMH_WAIT_EXEC);
-out:
-	return err;
-}
-EXPORT_SYMBOL_GPL(fork_usermode_driver);
-
-

-- 
2.50.1

Re: [PATCH bpf-next 2/2] umd: Remove usermode driver framework

[Alexei Starovoitov]

On Mon, Jul 21, 2025 at 2:05 AM Thomas Weißschuh
<thomas.weissschuh@linutronix.de> wrote:
>
> The code is unused since commit 98e20e5e13d2 ("bpfilter: remove bpfilter"),
> remove it.

Correct, but we have plans to use it.
Since it's not causing any problems we prefer to keep it
to avoid reverting the removal later.

Re: [PATCH bpf-next 2/2] umd: Remove usermode driver framework

[Christoph Hellwig]

On Mon, Jul 21, 2025 at 08:51:22AM -0700, Alexei Starovoitov wrote:
> On Mon, Jul 21, 2025 at 2:05 AM Thomas Weißschuh
> <thomas.weissschuh@linutronix.de> wrote:
> >
> > The code is unused since commit 98e20e5e13d2 ("bpfilter: remove bpfilter"),
> > remove it.
> 
> Correct, but we have plans to use it.
> Since it's not causing any problems we prefer to keep it
> to avoid reverting the removal later.

Plans to eventually use something are no reason to keep code that's been
unused for almost 2 years around.  Unless the removal would conflict with
currently queued up in linux-next code it is always better to just drop
it and reinstate it when (or rather usually IFF) it is used again.

Re: [PATCH bpf-next 2/2] umd: Remove usermode driver framework

[Eric W. Biederman]

Christoph Hellwig <hch@lst.de> writes:

> On Mon, Jul 21, 2025 at 08:51:22AM -0700, Alexei Starovoitov wrote:
>> On Mon, Jul 21, 2025 at 2:05 AM Thomas Weißschuh
>> <thomas.weissschuh@linutronix.de> wrote:
>> >
>> > The code is unused since commit 98e20e5e13d2 ("bpfilter: remove bpfilter"),
>> > remove it.
>> 
>> Correct, but we have plans to use it.
>> Since it's not causing any problems we prefer to keep it
>> to avoid reverting the removal later.
>
> Plans to eventually use something are no reason to keep code that's been
> unused for almost 2 years around.  Unless the removal would conflict with
> currently queued up in linux-next code it is always better to just drop
> it and reinstate it when (or rather usually IFF) it is used again.

I wonder if those are the same plans that existed in June of 2020 when I
split out the usermode driver code from user mode helper?

As far as I know this code has never been seriously used, so I am in
favor of simplifying the maintenance burden.

Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>

Eric

Re: [PATCH bpf-next 2/2] umd: Remove usermode driver framework

[Christoph Hellwig]

On Mon, Jul 21, 2025 at 11:04:42AM +0200, Thomas Weißschuh wrote:
> The code is unused since commit 98e20e5e13d2 ("bpfilter: remove bpfilter"),

Overly long commit message here.

> remove it.

Otherwise looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH bpf-next 2/2] umd: Remove usermode driver framework

[Thomas Weißschuh]

On Tue, Jul 22, 2025 at 08:34:11AM +0200, Christoph Hellwig wrote:
> On Mon, Jul 21, 2025 at 11:04:42AM +0200, Thomas Weißschuh wrote:
> > The code is unused since commit 98e20e5e13d2 ("bpfilter: remove bpfilter"),
> 
> Overly long commit message here.

75 characters are allowed, no?

> > remove it.
> 
> Otherwise looks good:
> 
> Reviewed-by: Christoph Hellwig <hch@lst.de>

Thanks!

Re: [PATCH bpf-next 2/2] umd: Remove usermode driver framework

[Christoph Hellwig]

On Wed, Jul 23, 2025 at 09:01:16AM +0200, Thomas Weißschuh wrote:
> On Tue, Jul 22, 2025 at 08:34:11AM +0200, Christoph Hellwig wrote:
> > On Mon, Jul 21, 2025 at 11:04:42AM +0200, Thomas Weißschuh wrote:
> > > The code is unused since commit 98e20e5e13d2 ("bpfilter: remove bpfilter"),
> > 
> > Overly long commit message here.
> 
> 75 characters are allowed, no?

73.

Re: [PATCH bpf-next 2/2] umd: Remove usermode driver framework

[Thomas Weißschuh]

On Thu, Jul 24, 2025 at 09:29:18AM +0200, Christoph Hellwig wrote:
> On Wed, Jul 23, 2025 at 09:01:16AM +0200, Thomas Weißschuh wrote:
> > On Tue, Jul 22, 2025 at 08:34:11AM +0200, Christoph Hellwig wrote:
> > > On Mon, Jul 21, 2025 at 11:04:42AM +0200, Thomas Weißschuh wrote:
> > > > The code is unused since commit 98e20e5e13d2 ("bpfilter: remove bpfilter"),
> > > 
> > > Overly long commit message here.
> > 
> > 75 characters are allowed, no?
> 
> 73.

Documentation/process/submitting-patches.rst:

	The canonical patch message body contains the following:

	  (...)

	  - The body of the explanation, line wrapped at 75 columns, which will
	    be copied to the permanent changelog to describe this patch.


scripts/checkpatch.pl:

	# Check for line lengths > 75 in commit log, warn once
			if ($in_commit_log && !$commit_log_long_line &&
			    length($line) > 75 &&
			      (...)) {
				WARN("COMMIT_LOG_LONG_LINE",
				     "Prefer a maximum 75 chars per line (possible unwrapped commit description?)\n" . $herecurr);
				$commit_log_long_line = 1;
			}


What am I missing?

Re: [PATCH bpf-next 2/2] umd: Remove usermode driver framework

[Christoph Hellwig]

On Thu, Jul 24, 2025 at 10:38:19AM +0200, Thomas Weißschuh wrote:
> Documentation/process/submitting-patches.rst:
> 
> 	The canonical patch message body contains the following:
> 
> 	  (...)
> 
> 	  - The body of the explanation, line wrapped at 75 columns, which will
> 	    be copied to the permanent changelog to describe this patch.

Hmm, weird.  I always through we stuck to the usual email length,
because in the end that's what commit messages actually are.

But I guess I was wrong, at least since people added this.

Re: [PATCH bpf-next 2/2] umd: Remove usermode driver framework

[Christian Brauner]

On Tue, Jul 22, 2025 at 08:34:11AM +0200, Christoph Hellwig wrote:
> On Mon, Jul 21, 2025 at 11:04:42AM +0200, Thomas Weißschuh wrote:
> > The code is unused since commit 98e20e5e13d2 ("bpfilter: remove bpfilter"),
> 
> Overly long commit message here.
> 
> > remove it.
> 
> Otherwise looks good:
> 
> Reviewed-by: Christoph Hellwig <hch@lst.de>

Reviewed-by: Christian Brauner <brauner@kernel.org>

Re: [PATCH bpf-next 2/2] umd: Remove usermode driver framework

[Alexei Starovoitov]

On Wed, Jul 23, 2025 at 5:49 AM Christian Brauner <brauner@kernel.org> wrote:
>
> On Tue, Jul 22, 2025 at 08:34:11AM +0200, Christoph Hellwig wrote:
> > On Mon, Jul 21, 2025 at 11:04:42AM +0200, Thomas Weißschuh wrote:
> > > The code is unused since commit 98e20e5e13d2 ("bpfilter: remove bpfilter"),
> >
> > Overly long commit message here.
> >
> > > remove it.
> >
> > Otherwise looks good:
> >
> > Reviewed-by: Christoph Hellwig <hch@lst.de>
>
> Reviewed-by: Christian Brauner <brauner@kernel.org>

Fair enough. Democracy wins.
Will apply once I'm back from pto.

Re: [PATCH bpf-next 2/2] umd: Remove usermode driver framework

[Christian Brauner]

On Wed, Jul 23, 2025 at 10:27:42AM -0600, Alexei Starovoitov wrote:
> On Wed, Jul 23, 2025 at 5:49 AM Christian Brauner <brauner@kernel.org> wrote:
> >
> > On Tue, Jul 22, 2025 at 08:34:11AM +0200, Christoph Hellwig wrote:
> > > On Mon, Jul 21, 2025 at 11:04:42AM +0200, Thomas Weißschuh wrote:
> > > > The code is unused since commit 98e20e5e13d2 ("bpfilter: remove bpfilter"),
> > >
> > > Overly long commit message here.
> > >
> > > > remove it.
> > >
> > > Otherwise looks good:
> > >
> > > Reviewed-by: Christoph Hellwig <hch@lst.de>
> >
> > Reviewed-by: Christian Brauner <brauner@kernel.org>
> 
> Fair enough. Democracy wins.
> Will apply once I'm back from pto.

Fwiw, I honestly don't care that much. I think the removal makes sense
precisely because having unused code is usually not a good idea. If you
really want that infra you can always reintroduce it once someone
actually ends up using it.

Re: [PATCH bpf-next 0/2] umd: Remove usermode driver framework

[patchwork-bot+netdevbpf]

Hello:

This series was applied to bpf/bpf-next.git (master)
by Daniel Borkmann <daniel@iogearbox.net>:

On Mon, 21 Jul 2025 11:04:40 +0200 you wrote:
> The code is unused, remove it.
> 
> Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
> ---
> Thomas Weißschuh (2):
>       bpf/preload: Don't select USERMODE_DRIVER
>       umd: Remove usermode driver framework
> 
> [...]

Here is the summary with links:
  - [bpf-next,1/2] bpf/preload: Don't select USERMODE_DRIVER
    https://git.kernel.org/bpf/bpf-next/c/2b03164eee20
  - [bpf-next,2/2] umd: Remove usermode driver framework
    https://git.kernel.org/bpf/bpf-next/c/b7b3500bd4ee

You are awesome, thank you!
-- 
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