From nobody Wed Oct 8 14:36:59 2025 Received: from mail-pj1-f74.google.com (mail-pj1-f74.google.com [209.85.216.74]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1DBAC290BC8 for ; Fri, 27 Jun 2025 23:18:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.74 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1751066338; cv=none; b=WnDcKmd1rQBaq30GH7Dxu5+OKXEglb/6SNSIWnZuDt+Bzx+7d/QKiXoXTwM7VEhIxli/3sPV79cQfxaUGbo4Xt8deNvAwcHDUcJWLbi4TBbBSbgB2c29ERCjb4mtLHqf4al2y3goXaMZNRBXH/yo3YM52EJfErzo7VJnF4Za0X8= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1751066338; c=relaxed/simple; bh=zv535cnLSXE0Li+uSUzrbqjrIvtvJoeKTwTy0R3Hldw=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=XBF2QsWQJ7oa+hNsq3qovULpgzMHiDszo12T2F4sPEOHESpmQl/omKbsQL93kahxHUgK6jl8SPDSOB2gUo26adlE2DLBoVpt42b7rfCgnvGSI2Sli9lCMiK2waHY4WtQAPLfXNTdWlZEYKV+JHQB2vX2hSQ4jxk4rigJNi7KcaE= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--mmaurer.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=IE6kMU7z; arc=none smtp.client-ip=209.85.216.74 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--mmaurer.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="IE6kMU7z" Received: by mail-pj1-f74.google.com with SMTP id 98e67ed59e1d1-3132c8437ffso102359a91.1 for ; Fri, 27 Jun 2025 16:18:56 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1751066336; x=1751671136; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=XE7RB2hkCNj3GvqoAw6x/sKXqs8W0tVM52Lnf/rgWxo=; b=IE6kMU7z9VzMtZeWsXyFcqPKee4f2G8M+UoIwnbluugD6HfaesyqWSx3venFHJJQbh L5+G/Vn+3OLGMLWycySLPYYLZsrCIAHRPC/J1S/Kma/gFQAh4aSfjxBERTC4NbtF2l/8 +KnsYnSVXO9SyeG/j/zx+uReKEXyB4P5tQOO1+UpaXc0XrUg4PGf7Vb3Xv2OofkWhS40 nld+HSAVF/Ifv2bI0d03ZNPZZiYukLZOQVqkW3AsfkmNcc3r/sAy+VPqnH9+WJRsPy23 NQCyTABjibMvcOtx55GnaWsvxdqPyvHCHEJAhgrncdzRZJF1kTietk2nyR9YGrXfT4EX da8g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1751066336; x=1751671136; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=XE7RB2hkCNj3GvqoAw6x/sKXqs8W0tVM52Lnf/rgWxo=; b=l4nA/RMRfN4YFVowaAvBnljg6kLPJetVSEsDG1S26g5xsZJzRh1gsAQC025HW1KgHP HOwVSJMAqaPunZWDHncrwyWgs7ZpKgJ2bHaEMfRI7U45kfKsHYQBc9o7YuQz9tb2AJog 1n+Yxr+gO4seq1zqW+lpJv/cdV+IY8guABm0TpjqnPxIXB2FGr9Jd1RKmBIbBqlZ4dR4 QiMN1+NbF5lyTvMRQ+iZc67W8E+tVvma14xRmMYUtzMCf5YnDbXSDqiDxLrO3BQ0MsZX ila0PSbXzI4m/Iw4QMPrNlikuYLxO+7isYxJGBAON/AnIksUrRX/lNfM5a68F8Hx1nDf Yadg== X-Gm-Message-State: AOJu0Ywq32nTDLJGJF+VW4/lao6Ecy1L23xVTXMeJX9eulrs7Q8/AOx5 mg6Qxu55pJEiM1DbWFou+G5J9pYcRo3SRxC7DlGLvMWg5Rgrikiq6OfU7wlmNLkRUWSMEJPJy0D ddUNH4TTtrw== X-Google-Smtp-Source: AGHT+IF0ec7xiOhmnUZPpXxN0NzlLxCuAAWInLMq2oD00r3d/wF0waFCR+xNOm0giOGZ0ePdPkw6rSKh/4I8 X-Received: from pjbsl7.prod.google.com ([2002:a17:90b:2e07:b0:314:626:7b97]) (user=mmaurer job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90a:d603:b0:313:d79e:1f48 with SMTP id 98e67ed59e1d1-318c9243d32mr8295824a91.16.1751066336366; Fri, 27 Jun 2025 16:18:56 -0700 (PDT) Date: Fri, 27 Jun 2025 23:18:25 +0000 In-Reply-To: <20250627-debugfs-rust-v8-0-c6526e413d40@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250627-debugfs-rust-v8-0-c6526e413d40@google.com> X-Developer-Key: i=mmaurer@google.com; a=ed25519; pk=2Ezhl7+fEjTOMVFpplDeak2AdQ8cjJieLRVJdNzrW+E= X-Developer-Signature: v=1; a=ed25519-sha256; t=1751066331; l=7283; i=mmaurer@google.com; s=20250429; h=from:subject:message-id; bh=zv535cnLSXE0Li+uSUzrbqjrIvtvJoeKTwTy0R3Hldw=; b=HvJjD2UsDIdg39pm6QodxSwqYTnBxsNbWc4Syy7wT/pAesbHeXb5IqFZROPSV+FVvVWtGLpA4 feGOo3h5XxYA2oXw3LckbtrIW/9P2hlxotCVvxS1TNCOidkftnAc73j X-Mailer: b4 0.14.2 Message-ID: <20250627-debugfs-rust-v8-2-c6526e413d40@google.com> Subject: [PATCH v8 2/6] rust: debugfs: Bind file creation for long-lived Display From: Matthew Maurer To: Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , "=?utf-8?q?Bj=C3=B6rn_Roy_Baron?=" , Andreas Hindborg , Alice Ryhl , Trevor Gross , Danilo Krummrich , Greg Kroah-Hartman , "Rafael J. Wysocki" , Sami Tolvanen , Timur Tabi , Benno Lossin Cc: linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org, Matthew Maurer , Dirk Behme Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Allows creation of files for references that live forever and lack metadata through the `Display` implementation. The `Display` implementation is used because `seq_printf` needs to route through `%pA`, which in turn routes through Arguments. Tested-by: Dirk Behme Signed-off-by: Matthew Maurer --- rust/kernel/debugfs.rs | 62 +++++++++++++++++++++++++++++++++= ++++ rust/kernel/debugfs/display_file.rs | 61 +++++++++++++++++++++++++++++++++= +++ rust/kernel/debugfs/entry.rs | 8 +++++ 3 files changed, 131 insertions(+) diff --git a/rust/kernel/debugfs.rs b/rust/kernel/debugfs.rs index 2359bd11cd664fb9f7206f8fe38f758dc43d2cb8..1f20d85da56fcb89476552feefc= 9d97fab43cc04 100644 --- a/rust/kernel/debugfs.rs +++ b/rust/kernel/debugfs.rs @@ -10,7 +10,10 @@ use crate::str::CStr; #[cfg(CONFIG_DEBUG_FS)] use crate::sync::Arc; +use core::fmt::Display; =20 +#[cfg(CONFIG_DEBUG_FS)] +mod display_file; #[cfg(CONFIG_DEBUG_FS)] mod entry; #[cfg(CONFIG_DEBUG_FS)] @@ -59,6 +62,43 @@ fn create(_name: &CStr, _parent: Option<&Dir>) -> Self { Self() } =20 + #[cfg(CONFIG_DEBUG_FS)] + fn create_file(&self, name: &CStr, data: &'static = T) -> File { + let Some(parent) =3D &self.0 else { + return File { + _entry: Entry::empty(), + }; + }; + // SAFETY: + // * `name` is a NUL-terminated C string, living across the call, = by `CStr` invariant. + // * `parent` is a live `dentry` since we have a reference to it. + // * `vtable` is all stock `seq_file` implementations except for `= open`. + // `open`'s only requirement beyond what is provided to all open= functions is that the + // inode's data pointer must point to a `T` that will outlive it= , which we know because + // we have a static reference. + let ptr =3D unsafe { + bindings::debugfs_create_file_full( + name.as_char_ptr(), + 0o444, + parent.as_ptr(), + data as *const _ as *mut _, + core::ptr::null(), + &::VTABLE, + ) + }; + + // SAFETY: `debugfs_create_file_full` either returns an error code= or a legal + // dentry pointer, so `Entry::new` is safe to call here. + let entry =3D unsafe { Entry::new(ptr, Some(parent.clone())) }; + + File { _entry: entry } + } + + #[cfg(not(CONFIG_DEBUG_FS))] + fn create_file(&self, _name: &CStr, _data: &'stati= c T) -> File { + File {} + } + /// Create a DebugFS subdirectory. /// /// Subdirectory handles cannot outlive the directory handle they were= created from. @@ -75,6 +115,22 @@ pub fn subdir(&self, name: &CStr) -> Self { Dir::create(name, Some(self)) } =20 + /// Create a file in a DebugFS directory with the provided name, and c= ontents from invoking + /// [`Display::fmt`] on the provided reference. + /// + /// # Examples + /// + /// ``` + /// # use kernel::c_str; + /// # use kernel::debugfs::Dir; + /// let dir =3D Dir::new(c_str!("my_debugfs_dir")); + /// dir.display_file(c_str!("foo"), &200); + /// // "my_debugfs_dir/foo" now contains the number 200. + /// ``` + pub fn display_file(&self, name: &CStr, data: &'st= atic T) -> File { + self.create_file(name, data) + } + /// Create a new directory in DebugFS at the root. /// /// # Examples @@ -88,3 +144,9 @@ pub fn new(name: &CStr) -> Self { Dir::create(name, None) } } + +/// Handle to a DebugFS file. +pub struct File { + #[cfg(CONFIG_DEBUG_FS)] + _entry: Entry, +} diff --git a/rust/kernel/debugfs/display_file.rs b/rust/kernel/debugfs/disp= lay_file.rs new file mode 100644 index 0000000000000000000000000000000000000000..e4b551f7092884ad12e18a32cc2= 43d0d037931a6 --- /dev/null +++ b/rust/kernel/debugfs/display_file.rs @@ -0,0 +1,61 @@ +// SPDX-License-Identifier: GPL-2.0 +// Copyright (C) 2025 Google LLC. + +use crate::prelude::*; +use crate::seq_file::SeqFile; +use crate::seq_print; +use core::fmt::Display; + +/// Implements `open` for `file_operations` via `single_open` to fill out = a `seq_file`. +/// +/// # Safety +/// +/// * `inode`'s private pointer must point to a value of type `T` which wi= ll outlive the `inode` +/// and will not be mutated during this call. +/// * `file` must point to a live, not-yet-initialized file object. +pub(crate) unsafe extern "C" fn display_open( + inode: *mut bindings::inode, + file: *mut bindings::file, +) -> c_int { + // SAFETY: + // * `file` is acceptable by caller precondition. + // * `print_act` will be called on a `seq_file` with private data set = to the third argument, + // so we meet its safety requirements. + // * The `data` pointer passed in the third argument is a valid `T` po= inter that outlives + // this call by caller preconditions. + unsafe { bindings::single_open(file, Some(display_act::), (*inode).= i_private) } +} + +/// Prints private data stashed in a seq_file to that seq file. +/// +/// # Safety +/// +/// `seq` must point to a live `seq_file` whose private data is a live poi= nter to a `T` which is +/// not being mutated. +pub(crate) unsafe extern "C" fn display_act( + seq: *mut bindings::seq_file, + _: *mut c_void, +) -> c_int { + // SAFETY: By caller precondition, this pointer is live, points to a v= alue of type `T`, and + // is not being mutated. + let data =3D unsafe { &*((*seq).private as *mut T) }; + // SAFETY: By caller precondition, `seq_file` points to a live `seq_fi= le`, so we can lift + // it. + let seq_file =3D unsafe { SeqFile::from_raw(seq) }; + seq_print!(seq_file, "{}", data); + 0 +} + +// Work around lack of generic const items. +pub(crate) trait DisplayFile: Display + Sized { + const VTABLE: bindings::file_operations =3D bindings::file_operations { + read: Some(bindings::seq_read), + llseek: Some(bindings::seq_lseek), + release: Some(bindings::single_release), + open: Some(display_open::), + // SAFETY: `file_operations` supports zeroes in all fields. + ..unsafe { core::mem::zeroed() } + }; +} + +impl DisplayFile for T {} diff --git a/rust/kernel/debugfs/entry.rs b/rust/kernel/debugfs/entry.rs index ae0e2c4e1d58e878ebb081a71e4ac0f4a7d99b91..2baaf31c326c3071b92b5bc3755= 2907fa1102246 100644 --- a/rust/kernel/debugfs/entry.rs +++ b/rust/kernel/debugfs/entry.rs @@ -38,6 +38,14 @@ pub(crate) unsafe fn new(entry: *mut bindings::dentry, p= arent: Option } } =20 + /// Constructs a placeholder DebugFS [`Entry`]. + pub(crate) fn empty() -> Self { + Self { + entry: core::ptr::null_mut(), + _parent: None, + } + } + /// Returns the pointer representation of the DebugFS directory. /// /// # Guarantees --=20 2.50.0.727.gbf7dc18ff4-goog