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

Jonathan Cameron
2024-07-01T15:07:12Z

On Mon, 24 Jun 2024 11:19:19 +0200
Mauro Carvalho Chehab <mchehab+huawei@kernel.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@kernel.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 *,