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    SubjectRe: [PATCH v2 1/3] lib: bitmap: introduce bitmap_print_to_buf
    On Wed, 2 Jun 2021 21:48:52 +0800
    Tian Tao <tiantao6@hisilicon.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@hisilicon.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);
    >

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