linux-kernel - Re: [PATCH v5 2/4] efi/cper: Add a new helper function to print bitmasks

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Message-ID: <20240701160709.000064c6@Huawei.com>
Date: Mon, 1 Jul 2024 16:07:09 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
CC: Borislav Petkov <bp@...en8.de>, James Morse <james.morse@....com>, Shiju
 Jose <shiju.jose@...wei.com>, Tony Luck <tony.luck@...el.com>, Alison
 Schofield <alison.schofield@...el.com>, Ard Biesheuvel <ardb@...nel.org>,
	Dave Jiang <dave.jiang@...el.com>, Ira Weiny <ira.weiny@...el.com>,
	<linux-edac@...r.kernel.org>, <linux-efi@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 2/4] efi/cper: Add a new helper function to print
 bitmasks

On Mon, 24 Jun 2024 11:19:19 +0200
Mauro Carvalho Chehab <mchehab+huawei@...nel.org> wrote:

> Sometimes it is desired to produce a single log line for errors.

This description is a bit cryptic.  Maybe an example would make
it easier for anyone coming across this in the future?

> Add a new helper function for such purpose.
> 
> Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
Minor comment inline.

> ---
>  drivers/firmware/efi/cper.c | 41 +++++++++++++++++++++++++++++++++++++
>  include/linux/cper.h        |  2 ++
>  2 files changed, 43 insertions(+)
> 
> diff --git a/drivers/firmware/efi/cper.c b/drivers/firmware/efi/cper.c
> index 7d2cdd9e2227..4cf56657afde 100644
> --- a/drivers/firmware/efi/cper.c
> +++ b/drivers/firmware/efi/cper.c
> @@ -106,6 +106,47 @@ void cper_print_bits(const char *pfx, unsigned int bits,
>  		printk("%s\n", buf);
>  }
>  
> +/*
> + * cper_bits_to_str - return a string for set bits
> + * @buf: buffer to store the output string
> + * @buf_size: size of the output string buffer
> + * @bits: bit mask
> + * @strs: string array, indexed by bit position
> + * @strs_size: size of the string array: @strs
> + * @mask: a continuous bitmask used to detect the first valid bit of the
> + *        bitmap.
> + *
> + * Add to @buf the bitmask in hexadecimal. Then, for each set bit in @bits
> + * mask, add the corresponding string describing the bit in @strs to @buf.
> + */
> +char *cper_bits_to_str(char *buf, int buf_size, unsigned long bits,
> +		       const char * const strs[], unsigned int strs_size)
> +{
> +	int len = buf_size;
> +	char *str = buf;
> +	int i, size;
> +
> +	for_each_set_bit(i, &bits, strs_size) {
> +		if (!(bits & (1U << (i))))
> +			continue;
> +
> +		if (*buf && len > 0) {

That first check on *buf is a bit esoteric.
It's more than possible we get a non clear
buffer passed in.  I'd just use a
	bool first = true;
...
		if (!first && len > 0) {
			*str = '|';
			len--;
			str++;
		}
		first = false;


> +			*str = '|';
> +			len--;
> +			str++;
> +		}
> +
> +		size = strscpy(str, strs[i], len);
> +		if (size < 0)
> +			break;
> +
> +		len -= size;
> +		str += size;
> +	}
> +	return buf;

Why return buf?  You never use it and it's not entirely obvious
that is the right thing to return (as opposed to length written for example).

> +}
> +EXPORT_SYMBOL_GPL(cper_bits_to_str);
> +
>  static const char * const proc_type_strs[] = {
>  	"IA32/X64",
>  	"IA64",
> diff --git a/include/linux/cper.h b/include/linux/cper.h
> index 265b0f8fc0b3..c2f14b916bfb 100644
> --- a/include/linux/cper.h
> +++ b/include/linux/cper.h
> @@ -584,6 +584,8 @@ const char *cper_mem_err_type_str(unsigned int);
>  const char *cper_mem_err_status_str(u64 status);
>  void cper_print_bits(const char *prefix, unsigned int bits,
>  		     const char * const strs[], unsigned int strs_size);
> +char *cper_bits_to_str(char *buf, int buf_size, unsigned long bits,
> +		       const char * const strs[], unsigned int strs_size);
>  void cper_mem_err_pack(const struct cper_sec_mem_err *,
>  		       struct cper_mem_err_compact *);
>  const char *cper_mem_err_unpack(struct trace_seq *,