James Bottomley <jbottom...@odin.com> writes: > On Thu, 2015-10-29 at 17:30 +0100, Vitaly Kuznetsov wrote: >> string_get_size() can't really handle huge block sizes, especially >> blk_size > U32_MAX but string_get_size() interface states the opposite. >> Change blk_size from u64 to u32 to reflect the reality. > > What is the actual evidence for this? The calculation is designed to be > a symmetric 128 bit multiply. When I wrote and tested it, it worked > fine for huge block sizes.
We have 'u32 remainder' and then we do: exp = divisor[units] / (u32)blk_size; ... remainder = do_div(size, divisor[units]); remainder *= blk_size; I'm pretty sure it will overflow for some inputs. > > James > >> Signed-off-by: Vitaly Kuznetsov <vkuzn...@redhat.com> >> --- >> include/linux/string_helpers.h | 2 +- >> lib/string_helpers.c | 4 ++-- >> 2 files changed, 3 insertions(+), 3 deletions(-) >> >> diff --git a/include/linux/string_helpers.h b/include/linux/string_helpers.h >> index dabe643..1223e80 100644 >> --- a/include/linux/string_helpers.h >> +++ b/include/linux/string_helpers.h >> @@ -10,7 +10,7 @@ enum string_size_units { >> STRING_UNITS_2, /* use binary powers of 2^10 */ >> }; >> >> -void string_get_size(u64 size, u64 blk_size, enum string_size_units units, >> +void string_get_size(u64 size, u32 blk_size, enum string_size_units units, >> char *buf, int len); >> >> #define UNESCAPE_SPACE 0x01 >> diff --git a/lib/string_helpers.c b/lib/string_helpers.c >> index 5939f63..f6c27dc 100644 >> --- a/lib/string_helpers.c >> +++ b/lib/string_helpers.c >> @@ -26,7 +26,7 @@ >> * at least 9 bytes and will always be zero terminated. >> * >> */ >> -void string_get_size(u64 size, u64 blk_size, const enum string_size_units >> units, >> +void string_get_size(u64 size, u32 blk_size, const enum string_size_units >> units, >> char *buf, int len) >> { >> static const char *const units_10[] = { >> @@ -58,7 +58,7 @@ void string_get_size(u64 size, u64 blk_size, const enum >> string_size_units units, >> i++; >> } >> >> - exp = divisor[units] / (u32)blk_size; >> + exp = divisor[units] / blk_size; >> /* >> * size must be strictly greater than exp here to ensure that remainder >> * is greater than divisor[units] coming out of the if below. -- Vitaly -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/