Messages in this thread | | | Date | Tue, 22 Feb 2022 10:06:36 +0100 | From | Petr Mladek <> | Subject | Re: [PATCH v4 10/20] rust: add `kernel` crate |
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On Sat 2022-02-12 14:03:36, Miguel Ojeda wrote: > From: Wedson Almeida Filho <wedsonaf@google.com> > > The `kernel` crate currently includes all the abstractions that wrap > kernel features written in C. > > These abstractions call the C side of the kernel via the generated > bindings with the `bindgen` tool. Modules developed in Rust should > never call the bindings themselves. > > In the future, as the abstractions grow in number, we may need > to split this crate into several, possibly following a similar > subdivision in subsystems as the kernel itself and/or moving > the code to the actual subsystems. > > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c > index 82abfaf3c2aa..c042386667f2 100644 > --- a/kernel/printk/printk.c > +++ b/kernel/printk/printk.c > @@ -392,7 +392,10 @@ static struct latched_seq clear_seq = { > /* the maximum size of a formatted record (i.e. with prefix added per line) */ > #define CONSOLE_LOG_MAX 1024 > > -/* the maximum size allowed to be reserved for a record */ > +/* > + * The maximum size allowed to be reserved for a record. > + * Keep in sync with rust/kernel/print.rs. > + */ > #define LOG_LINE_MAX (CONSOLE_LOG_MAX - PREFIX_MAX)
What exactly should we keep in sync, please?
I see only handling of KERN_* prefix in print.rs. I do not see there any counter part of LOG_LINE_MAX, CONSOLE_LOG_MAX, or PREFIX_MAX.
Also note that PREFIX_MAX is the maximal lenght of the prefix printed on console. It is log level + time stamp + caller id. For example:
<12>[ 123.632345][ T3260]
It seems that print.rs defines max size of the prefix in the printk format where the log level is defined using KERN_* pair of characters.
> > #define LOG_LEVEL(v) ((v) & 0x07) > diff --git a/rust/kernel/print.rs b/rust/kernel/print.rs > new file mode 100644 > index 000000000000..dba4ef10c722 > --- /dev/null > +++ b/rust/kernel/print.rs > @@ -0,0 +1,417 @@ > +/// Format strings. > +/// > +/// Public but hidden since it should only be used from public macros. > +#[doc(hidden)] > +pub mod format_strings { > + use crate::bindings; > + > + /// The length we copy from the `KERN_*` kernel prefixes. > + const LENGTH_PREFIX: usize = 2; > + > + /// The length of the fixed format strings. > + pub const LENGTH: usize = 10;
I am sorry but I am not familiar with rust. What are these limits 2 and 10 used for, please?
I guess that 2 is the size of a single KERN_* identifier. But what is 10?
Note that printk() format prefix is typically just a single KERN_* identifier. But there might be more. Well, in practice only the following combination makes sense: KERN_CONT + KERN_<LEVEL>.
> + /// Generates a fixed format string for the kernel's [`_printk`]. > + /// > + /// The format string is always the same for a given level, i.e. for a > + /// given `prefix`, which are the kernel's `KERN_*` constants. > + /// > + /// [`_printk`]: ../../../../include/linux/printk.h > + const fn generate(is_cont: bool, prefix: &[u8; 3]) -> [u8; LENGTH] { > + // Ensure the `KERN_*` macros are what we expect. > + assert!(prefix[0] == b'\x01'); > + if is_cont { > + assert!(prefix[1] == b'c'); > + } else { > + assert!(prefix[1] >= b'0' && prefix[1] <= b'7'); > + } > + assert!(prefix[2] == b'\x00'); > + > + let suffix: &[u8; LENGTH - LENGTH_PREFIX] = if is_cont { > + b"%pA\0\0\0\0\0" > + } else { > + b"%s: %pA\0" > + }; > + > + [ > + prefix[0], prefix[1], suffix[0], suffix[1], suffix[2], suffix[3], suffix[4], suffix[5], > + suffix[6], suffix[7], > + ] > + }
Finally, is there any way to test whether any change in the printk code breaks the rust support?
Best Regards, Petr
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