On 16/10/20 6:16 am, Alan Cudmore wrote: > On Thu, Oct 15, 2020 at 3:03 PM Chris Johns <chr...@rtems.org> wrote: >> The number of bits needs to align to a value that fits the whole 32 bit mask >> so >> the last is used to trigger the bug. > > How can I calculate this?
The number of bits in a bitmap is the number of blocks in the file system. The search bit map is a bit for every 32 bits of the block bit map. Therefore 32 bits of the search bit map covers 32 x 32 or 1024 blocks. The RFS can search 1024 blocks of the file system for a free block with a single 32 bit test. A file system with 4096 blocks will have 4 search bit map elements (as defined in the RFS). The buffer overflow will happen if the "(blocks % 1024) == 0" > It would be great if I could tell known > users that they don't need to worry about it. Yes this is a good approach. > For example, in the open source cFS bundle where I encountered the > issue, it creates an RFS formatted RAM disk that is 0x200000 bytes in > size (2 Mbytes). I would imagine that is a nice round number of bitmap > elements. It depends on the block size as well as that determines the number of blocks. Chris _______________________________________________ devel mailing list devel@rtems.org http://lists.rtems.org/mailman/listinfo/devel
