Re: [PATCH v2] bitmap: remove explicit newline handling using scnprintf format string
From: Andrew Morton
Date: Wed Apr 29 2015 - 18:48:45 EST
On Tue, 28 Apr 2015 16:36:41 +0100 Sudeep Holla <sudeep.holla@xxxxxxx> wrote:
> bitmap_print_to_pagebuf uses scnprintf to copy the cpumask/list to page
> buffer. It handles the newline and trailing null character explicitly.
bitmap_print_to_pagebuf() is horrid :( That automagic "assume caller
passed us an offset into a PAGE_SIZE area".
> It's unnecessary and also partially duplicated as scnprintf already adds
> trailing null character. The newline can be passed through format string
> to scnprintf. This patch does that simplification.
> However theoritically there's one behavior difference: when the buffer
> is too small, the original code would still output '\n' at the end while
> the new code(with this patch) would just continue to print the formatted
> string. Since this function is dealing with only page buffers, it's
> highly unlikely to hit that corner case.
> This patch will help in auditing the users of bitmap_print_to_pagebuf
> to verify that the buffer passed is large enough and get rid of it
> completely by replacing them with direct scnprintf()
Yes, bitmap_print_to_pagebuf() should be eliminated. Make the callers
keep track of how much room they have in their buffer.
> --- a/lib/bitmap.c
> +++ b/lib/bitmap.c
> @@ -462,19 +462,18 @@ EXPORT_SYMBOL(bitmap_parse_user);
> * Output format is a comma-separated list of decimal numbers and
> * ranges if list is specified or hex digits grouped into comma-separated
> * sets of 8 digits/set. Returns the number of characters written to buf.
> + * It is assumed that the buffer passed is atleast PAGE_SIZE and easily
> + * accommodate nmaskbits.
How does this look?
@@ -462,8 +462,10 @@ EXPORT_SYMBOL(bitmap_parse_user);
* Output format is a comma-separated list of decimal numbers and
* ranges if list is specified or hex digits grouped into comma-separated
* sets of 8 digits/set. Returns the number of characters written to buf.
- * It is assumed that the buffer passed is atleast PAGE_SIZE and easily
- * accommodate nmaskbits.
+ * It is assumed that @buf is a pointer into a PAGE_SIZE area and that
+ * sufficient storage remains at @buf to accommodate the
+ * bitmap_print_to_pagebuf() output.
int bitmap_print_to_pagebuf(bool list, char *buf, const unsigned long *maskp,
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