linux-kernel - Re: [PATCH v2 1/3] lib: bitmap: introduce bitmap_print_to

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Message-ID: <20210602152217.00007f13@Huawei.com>
Date:   Wed, 2 Jun 2021 15:22:17 +0100
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Tian Tao <tiantao6@...ilicon.com>
CC:     <gregkh@...uxfoundation.org>, <rafael@...nel.org>,
        <andriy.shevchenko@...ux.intel.com>, <akpm@...ux-foundation.org>,
        <song.bao.hua@...ilicon.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] lib: bitmap: introduce bitmap_print_to_buf

On Wed, 2 Jun 2021 21:48:52 +0800
Tian Tao <tiantao6@...ilicon.com> wrote:

> New API bitmap_print_to_buf() with bin_attribute to avoid maskp
> exceeding PAGE_SIZE. bitmap_print_to_pagebuf() is a special case
> of bitmap_print_to_buf(), so in bitmap_print_to_pagebuf() call
> bitmap_print_to_buf().
> 
> Signed-off-by: Tian Tao <tiantao6@...ilicon.com>
Hi,

I think you need strlen() + 1 as strlen() doesn't include the null terminator.
Also good to add () in a few more places to make the hyperlinks work in the
html docs (fairly sure it needs those)

I don't really like the fact we can't get the string length without that
extra call (as it's buried in the kasprintf() implementation) but this is
unlikely to be a high performance path so clean code is better.

Otherwise, LGTM

> ---
>  include/linux/bitmap.h  |  3 +++
>  include/linux/cpumask.h | 21 +++++++++++++++++++++
>  lib/bitmap.c            | 38 ++++++++++++++++++++++++++++++++++++--
>  3 files changed, 60 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
> index 70a9324..bc401bd9b 100644
> --- a/include/linux/bitmap.h
> +++ b/include/linux/bitmap.h
> @@ -219,6 +219,9 @@ extern unsigned int bitmap_ord_to_pos(const unsigned long *bitmap, unsigned int
>  extern int bitmap_print_to_pagebuf(bool list, char *buf,
>  				   const unsigned long *maskp, int nmaskbits);
>  
> +extern int bitmap_print_to_buf(bool list, char *buf,
> +			       const unsigned long *maskp, int nmaskbits, loff_t off, size_t count);
> +
>  #define BITMAP_FIRST_WORD_MASK(start) (~0UL << ((start) & (BITS_PER_LONG - 1)))
>  #define BITMAP_LAST_WORD_MASK(nbits) (~0UL >> (-(nbits) & (BITS_PER_LONG - 1)))
>  
> diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
> index 383684e..56852f2 100644
> --- a/include/linux/cpumask.h
> +++ b/include/linux/cpumask.h
> @@ -928,6 +928,27 @@ cpumap_print_to_pagebuf(bool list, char *buf, const struct cpumask *mask)
>  				      nr_cpu_ids);
>  }
>  
> +/**
> + * cpumap_print_to_buf  - copies the cpumask into the buffer either
> + *      as comma-separated list of cpus or hex values of cpumask
> + * @list: indicates whether the cpumap must be list
> + * @mask: the cpumask to copy
> + * @buf: the buffer to copy into
> + * @off: in the string from which we are copying, We copy to @buf + off
> + * @count: the maximum number of bytes to print
> + *
> + * The role of cpumap_print_to_buf and cpumap_print_to_pagebuf is

cpumap_print_to_buf()
+ other cases of the same so that hyperlinks work in the html docs.


> + * the same, the difference is that buf of bitmap_print_to_buf
> + * can be more than one pagesize.
> + */
> +static inline ssize_t
> +cpumap_print_to_buf(bool list, char *buf, const struct cpumask *mask,
> +		    loff_t off, size_t count)
> +{
> +	return bitmap_print_to_buf(list, buf, cpumask_bits(mask),
> +				   nr_cpu_ids, off, count);
> +}
> +
>  #if NR_CPUS <= BITS_PER_LONG
>  #define CPU_MASK_ALL							\
>  (cpumask_t) { {								\
> diff --git a/lib/bitmap.c b/lib/bitmap.c
> index 75006c4..cb64e66 100644
> --- a/lib/bitmap.c
> +++ b/lib/bitmap.c
> @@ -460,6 +460,40 @@ int bitmap_parse_user(const char __user *ubuf,
>  EXPORT_SYMBOL(bitmap_parse_user);
>  
>  /**
> + * bitmap_print_to_buf - convert bitmap to list or hex format ASCII string
> + * @list: indicates whether the bitmap must be list
> + * @buf: the kernel space buffer to read to
> + * @maskp: pointer to bitmap to convert
> + * @nmaskbits: size of bitmap, in bits
> + * @off: offset in data buffer below
> + * @count: the maximum number of bytes to print
> + *
> + * The role of bitmap_print_to_buf and bitmap_print_to_pagebuf() is
> + * the same, the difference is that buf of bitmap_print_to_buf()
> + * can be more than one pagesize.
> + */
> +int bitmap_print_to_buf(bool list, char *buf, const unsigned long *maskp,
> +			int nmaskbits, loff_t off, size_t count)
> +{
> +	int size;
> +	void *data;
> +	const char *fmt = list ? "%*pbl\n" : "%*pb\n";
> +
> +	if (off == LLONG_MAX && count == PAGE_SIZE - offset_in_page(buf))
> +		return scnprintf(buf, count, fmt, nmaskbits, maskp);
> +
> +	data = kasprintf(GFP_KERNEL, fmt, nmaskbits, maskp);
> +	if (!data)
> +		return -ENOMEM;
> +
> +	size = memory_read_from_buffer(buf, count, &off, data, strlen(data));

strlen(data) + 1 I think...

> +	kfree(data);
> +
> +	return size;
> +}
> +EXPORT_SYMBOL(bitmap_print_to_buf);
> +
> +/**
>   * bitmap_print_to_pagebuf - convert bitmap to list or hex format ASCII string
>   * @list: indicates whether the bitmap must be list
>   * @buf: page aligned buffer into which string is placed
> @@ -480,8 +514,8 @@ int bitmap_print_to_pagebuf(bool list, char *buf, const unsigned long *maskp,
>  {
>  	ptrdiff_t len = PAGE_SIZE - offset_in_page(buf);
>  
> -	return list ? scnprintf(buf, len, "%*pbl\n", nmaskbits, maskp) :
> -		      scnprintf(buf, len, "%*pb\n", nmaskbits, maskp);
> +	return bitmap_print_to_buf(list, buf, maskp, nmaskbits,
> +				   LLONG_MAX, len);
>  }
>  EXPORT_SYMBOL(bitmap_print_to_pagebuf);
>