New printing support

Features:

  - Adds macros like `info!` (with newline) and `pr_info!` (without
    newline) for the usual levels that the kernel support.

  - Includes the "continuation" level.

  - Includes automatically the module name in the string.

  - Includes, hopefully, pretty detailed logs.

  - Includes aliases to make it even easier to find the equivalent to
    `println!` for newcomers.

Implementation:

  - Stack usage should be 1 KiB at most, regardless of the number of
    invocations of the macro in a single function. This should make
    it possible to use even when optimizations are not enabled.
    See code comments for the details.

  - The formatting string is compile-time, shared as a `static`,
    and always the same. We could perhaps pre-generate them
    per-module to avoid another `%.*s` in `printk()`, but I don't
    think it is worth the complexity at the moment, and it would
    increase memory usage anyway.

Naming:

  - The `pr_*` names are the same as the kernel ones, and behave
    similarly, i.e. no newline at the end.

  - The non-`pr_*` ones are the same but without the prefix.
    They look better (shorter, no underscore), have the newline like
    `println!`, and they are what people should almost always use except
    if they need continuation. And they look pretty similar to the Rust
    `log` crate ones, too!

  - I think we can afford these short names (in the prelude, even!) since
    this is new code and nobody should be defining macros in the kernel
    with such short names, ever!

Future:

  - I will open an issue with a few things that can be added on top,
    similar to the kernel parameters feature.

  - When we have tidy support (or custom clippy lints), we can add
    one to find the pattern:

        pr_*("...\n", ...);

    and suggest the non-prefixed, non-newline version instead:

        *("...", "...");

Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: ojeda

.github/workflows/ci.yaml

@@ -1,7 +1,7 @@
 on:
   pull_request: {}
   push:
-    branches: [rust]
+    branches: [rust, print]
 
 jobs:
   ci:
@@ -166,11 +166,6 @@ jobs:
           cp samples/rust/rust_module_parameters.rs samples/rust/rust_module_parameters_loadable_default.rs
           cp samples/rust/rust_module_parameters.rs samples/rust/rust_module_parameters_loadable_custom.rs
 
-          sed -i 's:"  my_:"  built-in default my_:g' samples/rust/rust_module_parameters_builtin_default.rs
-          sed -i 's:"  my_:"  built-in custom  my_:g' samples/rust/rust_module_parameters_builtin_custom.rs
-          sed -i 's:"  my_:"  loadable default my_:g' samples/rust/rust_module_parameters_loadable_default.rs
-          sed -i 's:"  my_:"  loadable custom  my_:g' samples/rust/rust_module_parameters_loadable_custom.rs
-
           sed -i 's:rust_module_parameters:rust_module_parameters_builtin_default:g'  samples/rust/rust_module_parameters_builtin_default.rs
           sed -i 's:rust_module_parameters:rust_module_parameters_builtin_custom:g'   samples/rust/rust_module_parameters_builtin_custom.rs
           sed -i 's:rust_module_parameters:rust_module_parameters_loadable_default:g' samples/rust/rust_module_parameters_loadable_default.rs
@@ -217,43 +212,94 @@ jobs:
 
       # Check
       - run: |
-          grep '] Rust minimal sample (init)$' qemu-stdout.log
-          grep '] Rust minimal sample (exit)$' qemu-stdout.log
-
-          grep '] Rust module parameters sample (init)$'           qemu-stdout.log
-          grep ']   built-in default my_bool:    true$'            qemu-stdout.log
-          grep ']   built-in default my_i32:     42$'              qemu-stdout.log
-          grep ']   built-in default my_str:     default str val$' qemu-stdout.log
-          grep ']   built-in default my_usize:   42$'              qemu-stdout.log
-          grep ']   built-in default my_array:   \[0, 1]$'         qemu-stdout.log
-          grep ']   built-in custom  my_bool:    false$'           qemu-stdout.log
-          grep ']   built-in custom  my_i32:     345543$'          qemu-stdout.log
-          grep ']   built-in custom  my_str:     🦀mod$'           qemu-stdout.log
-          grep ']   built-in custom  my_usize:   84$'              qemu-stdout.log
-          grep ']   built-in custom  my_array:   \[1, 2, 3]$'      qemu-stdout.log
-          grep ']   loadable default my_bool:    true$'            qemu-stdout.log
-          grep ']   loadable default my_i32:     42$'              qemu-stdout.log
-          grep ']   loadable default my_str:     default str val$' qemu-stdout.log
-          grep ']   loadable default my_usize:   42$'              qemu-stdout.log
-          grep ']   loadable default my_array:   \[0, 1]$'         qemu-stdout.log
-          grep ']   loadable custom  my_bool:    false$'           qemu-stdout.log
-          grep ']   loadable custom  my_i32:     345543$'          qemu-stdout.log
-          grep ']   loadable custom  my_str:     🦀mod$'           qemu-stdout.log
-          grep ']   loadable custom  my_usize:   84$'              qemu-stdout.log
-          grep ']   loadable custom  my_array:   \[1, 2, 3]$'      qemu-stdout.log
-          grep '] Rust module parameters sample (exit)$'           qemu-stdout.log
-
-          grep '] Rust synchronisation primitives sample (init)$' qemu-stdout.log
-          grep '] Rust synchronisation primitives sample (exit)$' qemu-stdout.log
-
-          grep '] Rust character device sample (init)$' qemu-stdout.log
-          grep '] Rust character device sample (exit)$' qemu-stdout.log
-
-          grep '] Rust miscellaneous device sample (init)$' qemu-stdout.log
-          grep '] Rust miscellaneous device sample (exit)$' qemu-stdout.log
-
-          grep '] Rust stack probing sample (init)$' qemu-stdout.log
-          grep '] Rust stack probing sample (exit)$' qemu-stdout.log
+          grep '] rust_minimal: Rust minimal sample (init)$' qemu-stdout.log
+          grep '] rust_minimal: Rust minimal sample (exit)$' qemu-stdout.log
+
+      - run: |
+          grep '] rust_print: Rust printing macros sample (init)$'                 qemu-stdout.log
+
+          grep '] rust_print: Emergency message (level 0) with newline w/o args$'  qemu-stdout.log
+          grep '] rust_print: Alert message (level 1) with newline w/o args$'      qemu-stdout.log
+          grep '] rust_print: Critical message (level 2) with newline w/o args$'   qemu-stdout.log
+          grep '] rust_print: Error message (level 3) with newline w/o args$'      qemu-stdout.log
+          grep '] rust_print: Warning message (level 4) with newline w/o args$'    qemu-stdout.log
+          grep '] rust_print: Notice message (level 5) with newline w/o args$'     qemu-stdout.log
+          grep '] rust_print: Info message (level 6) with newline w/o args$'       qemu-stdout.log
+          grep '] rust_print: A line that is continued with newline w/o args$'     qemu-stdout.log
+
+          grep '] rust_print: Emergency message (level 0) w/o newline w/o args$'   qemu-stdout.log
+          grep '] rust_print: Alert message (level 1) w/o newline w/o args$'       qemu-stdout.log
+          grep '] rust_print: Critical message (level 2) w/o newline w/o args$'    qemu-stdout.log
+          grep '] rust_print: Error message (level 3) w/o newline w/o args$'       qemu-stdout.log
+          grep '] rust_print: Warning message (level 4) w/o newline w/o args$'     qemu-stdout.log
+          grep '] rust_print: Notice message (level 5) w/o newline w/o args$'      qemu-stdout.log
+          grep '] rust_print: Info message (level 6) w/o newline w/o args$'        qemu-stdout.log
+          grep '] rust_print: A line that is continued w/o newline w/o args$'      qemu-stdout.log
+
+          grep '] rust_print: Emergency message (level 0) with newline with args$' qemu-stdout.log
+          grep '] rust_print: Alert message (level 1) with newline with args$'     qemu-stdout.log
+          grep '] rust_print: Critical message (level 2) with newline with args$'  qemu-stdout.log
+          grep '] rust_print: Error message (level 3) with newline with args$'     qemu-stdout.log
+          grep '] rust_print: Warning message (level 4) with newline with args$'   qemu-stdout.log
+          grep '] rust_print: Notice message (level 5) with newline with args$'    qemu-stdout.log
+          grep '] rust_print: Info message (level 6) with newline with args$'      qemu-stdout.log
+          grep '] rust_print: A line that is continued with newline with args$'    qemu-stdout.log
+
+          grep '] rust_print: Emergency message (level 0) w/o newline with args$'  qemu-stdout.log
+          grep '] rust_print: Alert message (level 1) w/o newline with args$'      qemu-stdout.log
+          grep '] rust_print: Critical message (level 2) w/o newline with args$'   qemu-stdout.log
+          grep '] rust_print: Error message (level 3) w/o newline with args$'      qemu-stdout.log
+          grep '] rust_print: Warning message (level 4) w/o newline with args$'    qemu-stdout.log
+          grep '] rust_print: Notice message (level 5) w/o newline with args$'     qemu-stdout.log
+          grep '] rust_print: Info message (level 6) w/o newline with args$'       qemu-stdout.log
+          grep '] rust_print: A line that is continued w/o newline with args$'     qemu-stdout.log
+
+          grep '] rust_print: Rust printing macros sample (exit)$'                 qemu-stdout.log
+
+      - run: |
+          grep '] rust_module_parameters: Rust module parameters sample (init)$'           qemu-stdout.log
+
+          grep '] rust_module_parameters_builtin_default:   my_bool:    true$'             qemu-stdout.log
+          grep '] rust_module_parameters_builtin_default:   my_i32:     42$'               qemu-stdout.log
+          grep '] rust_module_parameters_builtin_default:   my_str:     default str val$'  qemu-stdout.log
+          grep '] rust_module_parameters_builtin_default:   my_usize:   42$'               qemu-stdout.log
+          grep '] rust_module_parameters_builtin_default:   my_array:   \[0, 1]$'          qemu-stdout.log
+
+          grep '] rust_module_parameters_builtin_custom:   my_bool:    false$'             qemu-stdout.log
+          grep '] rust_module_parameters_builtin_custom:   my_i32:     345543$'            qemu-stdout.log
+          grep '] rust_module_parameters_builtin_custom:   my_str:     🦀mod$'             qemu-stdout.log
+          grep '] rust_module_parameters_builtin_custom:   my_usize:   84$'                qemu-stdout.log
+          grep '] rust_module_parameters_builtin_custom:   my_array:   \[1, 2, 3]$'        qemu-stdout.log
+
+          grep '] rust_module_parameters_loadable_default:   my_bool:    true$'            qemu-stdout.log
+          grep '] rust_module_parameters_loadable_default:   my_i32:     42$'              qemu-stdout.log
+          grep '] rust_module_parameters_loadable_default:   my_str:     default str val$' qemu-stdout.log
+          grep '] rust_module_parameters_loadable_default:   my_usize:   42$'              qemu-stdout.log
+          grep '] rust_module_parameters_loadable_default:   my_array:   \[0, 1]$'         qemu-stdout.log
+
+          grep '] rust_module_parameters_loadable_custom:   my_bool:    false$'            qemu-stdout.log
+          grep '] rust_module_parameters_loadable_custom:   my_i32:     345543$'           qemu-stdout.log
+          grep '] rust_module_parameters_loadable_custom:   my_str:     🦀mod$'            qemu-stdout.log
+          grep '] rust_module_parameters_loadable_custom:   my_usize:   84$'               qemu-stdout.log
+          grep '] rust_module_parameters_loadable_custom:   my_array:   \[1, 2, 3]$'       qemu-stdout.log
+
+          grep '] rust_module_parameters: Rust module parameters sample (exit)$'           qemu-stdout.log
+
+      - run: |
+          grep '] rust_sync: Rust synchronisation primitives sample (init)$' qemu-stdout.log
+          grep '] rust_sync: Rust synchronisation primitives sample (exit)$' qemu-stdout.log
+
+      - run: |
+          grep '] rust_chrdev: Rust character device sample (init)$' qemu-stdout.log
+          grep '] rust_chrdev: Rust character device sample (exit)$' qemu-stdout.log
+
+      - run: |
+          grep '] rust_miscdev: Rust miscellaneous device sample (init)$' qemu-stdout.log
+          grep '] rust_miscdev: Rust miscellaneous device sample (exit)$' qemu-stdout.log
+
+      - run: |
+          grep '] rust_stack_probing: Rust stack probing sample (init)$' qemu-stdout.log
+          grep '] rust_stack_probing: Rust stack probing sample (exit)$' qemu-stdout.log
 
       # Report
       - run: |

.github/workflows/kernel-arm64-debug.config

@@ -1421,6 +1421,7 @@ CONFIG_SAMPLES=y
 # CONFIG_SAMPLE_WATCHDOG is not set
 CONFIG_SAMPLES_RUST=y
 CONFIG_SAMPLE_RUST_MINIMAL=m
+CONFIG_SAMPLE_RUST_PRINT=m
 CONFIG_SAMPLE_RUST_MODULE_PARAMETERS=m
 CONFIG_SAMPLE_RUST_SYNC=m
 CONFIG_SAMPLE_RUST_CHRDEV=m

.github/workflows/kernel-arm64-release.config

@@ -1339,6 +1339,7 @@ CONFIG_SAMPLES=y
 # CONFIG_SAMPLE_WATCHDOG is not set
 CONFIG_SAMPLES_RUST=y
 CONFIG_SAMPLE_RUST_MINIMAL=m
+CONFIG_SAMPLE_RUST_PRINT=m
 CONFIG_SAMPLE_RUST_MODULE_PARAMETERS=m
 CONFIG_SAMPLE_RUST_SYNC=m
 CONFIG_SAMPLE_RUST_CHRDEV=m

.github/workflows/kernel-ppc64le-debug.config

@@ -1481,6 +1481,7 @@ CONFIG_SAMPLES=y
 # CONFIG_SAMPLE_WATCHDOG is not set
 CONFIG_SAMPLES_RUST=y
 CONFIG_SAMPLE_RUST_MINIMAL=m
+CONFIG_SAMPLE_RUST_PRINT=m
 CONFIG_SAMPLE_RUST_MODULE_PARAMETERS=m
 CONFIG_SAMPLE_RUST_SYNC=m
 CONFIG_SAMPLE_RUST_CHRDEV=m

.github/workflows/kernel-ppc64le-release.config

@@ -1443,6 +1443,7 @@ CONFIG_SAMPLES=y
 # CONFIG_SAMPLE_WATCHDOG is not set
 CONFIG_SAMPLES_RUST=y
 CONFIG_SAMPLE_RUST_MINIMAL=m
+CONFIG_SAMPLE_RUST_PRINT=m
 CONFIG_SAMPLE_RUST_MODULE_PARAMETERS=m
 CONFIG_SAMPLE_RUST_SYNC=m
 CONFIG_SAMPLE_RUST_CHRDEV=m

.github/workflows/kernel-x86_64-debug.config

@@ -1433,6 +1433,7 @@ CONFIG_SAMPLES=y
 # CONFIG_SAMPLE_WATCHDOG is not set
 CONFIG_SAMPLES_RUST=y
 CONFIG_SAMPLE_RUST_MINIMAL=m
+CONFIG_SAMPLE_RUST_PRINT=m
 CONFIG_SAMPLE_RUST_MODULE_PARAMETERS=m
 CONFIG_SAMPLE_RUST_SYNC=m
 CONFIG_SAMPLE_RUST_CHRDEV=m

.github/workflows/kernel-x86_64-release.config

@@ -1381,6 +1381,7 @@ CONFIG_SAMPLES=y
 # CONFIG_SAMPLE_WATCHDOG is not set
 CONFIG_SAMPLES_RUST=y
 CONFIG_SAMPLE_RUST_MINIMAL=m
+CONFIG_SAMPLE_RUST_PRINT=m
 CONFIG_SAMPLE_RUST_MODULE_PARAMETERS=m
 CONFIG_SAMPLE_RUST_SYNC=m
 CONFIG_SAMPLE_RUST_CHRDEV=m

.github/workflows/qemu-init.sh

@@ -3,6 +3,9 @@
 busybox insmod rust_minimal.ko
 busybox  rmmod rust_minimal.ko
 
+busybox insmod rust_print.ko
+busybox  rmmod rust_print.ko
+
 busybox insmod rust_module_parameters.ko
 busybox  rmmod rust_module_parameters.ko
 

.github/workflows/qemu-initramfs.desc

@@ -6,6 +6,7 @@ slink   /bin/sh       /bin/busybox                    0755 0 0
 file    /init         .github/workflows/qemu-init.sh  0755 0 0
 
 file    /rust_minimal.ko            samples/rust/rust_minimal.ko            0755 0 0
+file    /rust_print.ko              samples/rust/rust_print.ko              0755 0 0
 file    /rust_module_parameters.ko  samples/rust/rust_module_parameters.ko  0755 0 0
 file    /rust_sync.ko               samples/rust/rust_sync.ko               0755 0 0
 file    /rust_chrdev.ko             samples/rust/rust_chrdev.ko             0755 0 0

kernel/printk/printk.c

@@ -410,6 +410,8 @@ static u64 clear_seq;
 #else
 #define PREFIX_MAX		32
 #endif
+
+/* Keep in sync with rust/kernel/print.rs */
 #define LOG_LINE_MAX		(1024 - PREFIX_MAX)
 
 #define LOG_LEVEL(v)		((v) & 0x07)

rust/kernel/lib.rs

@@ -17,6 +17,7 @@
     alloc_error_handler,
     const_fn,
     const_mut_refs,
+    const_panic,
     try_reserve
 )]
 #![deny(clippy::complexity)]
@@ -47,7 +48,7 @@ pub mod miscdev;
 pub mod module_param;
 
 pub mod prelude;
-pub mod printk;
+pub mod print;
 pub mod random;
 mod static_assert;
 pub mod sync;
@@ -152,7 +153,7 @@ fn panic(_info: &PanicInfo) -> ! {
 ///
 /// fn test() {
 ///     // This prints `8`.
-///     println!("{}", offset_of!(Test, b));
+///     info!("{}", offset_of!(Test, b));
 /// }
 /// ```
 #[macro_export]
@@ -193,7 +194,7 @@ macro_rules! offset_of {
 ///     let b_ptr = &test.b;
 ///     let test_alias = unsafe { container_of!(b_ptr, Test, b) };
 ///     // This prints `true`.
-///     println!("{}", core::ptr::eq(&test, test_alias));
+///     info!("{}", core::ptr::eq(&test, test_alias));
 /// }
 /// ```
 #[macro_export]

rust/kernel/prelude.rs

@@ -15,4 +15,9 @@ pub use alloc::{borrow::ToOwned, string::String};
 
 pub use module::module;
 
-pub use super::{println, static_assert, KernelModule, KernelResult};
+pub use super::{alert, cont, crit, emerg, err, info, notice, warn};
+pub use super::{pr_alert, pr_cont, pr_crit, pr_emerg, pr_err, pr_info, pr_notice, pr_warn};
+
+pub use super::static_assert;
+
+pub use super::{KernelModule, KernelResult};