On Wed, 3 Jan 2007, Eric Blake wrote: > coreutils has the following, in src/system.h, used by cp, install, mv, du, > ls, stat... [snip] > For example, in cp, the following usage appears: [snip] > It sounds like we want to ensure that cygwin chooses ST_BLKSIZE at 64k > (optimal I/O size) but ST_NBLOCKS/ST_NBLOCKSIZE at the disk granularity (512).
I got lost in all the code details you presented above, but I confess to not trying very hard. I don't think changing the block size to 512 bytes is really necessary, though. These are the examples that I had in mind: newlib stdio http://cygwin.com/cgi-bin/cvsweb.cgi/src/newlib/libc/stdio/makebuf.c?rev=1.6&content-type=text/x-cvsweb-markup&cvsroot=src : #ifdef HAVE_BLKSIZE size = st.st_blksize <= 0 ? BUFSIZ : st.st_blksize; #else size = BUFSIZ; #endif [skip] #ifdef HAVE_BLKSIZE fp->_blksize = st.st_blksize; #else fp->_blksize = 1024; #endif which is used to size and fill the stdio buffer. and coreutils cp http://cvs.savannah.gnu.org/viewcvs/coreutils/src/copy.c?rev=1.223&root=coreutils&view=auto : /* Choose a suitable buffer size; it may be adjusted later. */ size_t buf_alignment = lcm (getpagesize (), sizeof (word)); size_t buf_alignment_slop = sizeof (word) + buf_alignment - 1; size_t buf_size = ST_BLKSIZE (sb); [skip] /* If not making a sparse file, try to use a more-efficient buffer size. */ if (! make_holes) { /* These days there's no point ever messing with buffers smaller than 8 KiB. It would be nice to configure SMALL_BUF_SIZE dynamically for this host and pair of files, but there doesn't seem to be a good way to get readahead info portably. */ enum { SMALL_BUF_SIZE = 8 * 1024 }; /* Compute the least common multiple of the input and output buffer sizes, adjusting for outlandish values. */ size_t blcm_max = MIN (SIZE_MAX, SSIZE_MAX) - buf_alignment_slop; size_t blcm = buffer_lcm (ST_BLKSIZE (src_open_sb), buf_size, blcm_max); /* Do not use a block size that is too small. */ buf_size = MAX (SMALL_BUF_SIZE, blcm); /* Do not bother with a buffer larger than the input file, plus one byte to make sure the file has not grown while reading it. */ if (S_ISREG (src_open_sb.st_mode) && src_open_sb.st_size < buf_size) buf_size = src_open_sb.st_size + 1; /* However, stick with a block size that is a positive multiple of blcm, overriding the above adjustments. Watch out for overflow. */ buf_size += blcm - 1; buf_size -= buf_size % blcm; if (buf_size == 0 || blcm_max < buf_size) buf_size = blcm; } -- Brian Ford Lead Realtime Software Engineer VITAL - Visual Simulation Systems FlightSafety International the best safety device in any aircraft is a well-trained crew...
