Re: [libvirt] [PATCHv2 11/16] save: let iohelper work on O_DIRECT fds

Required for a coming patch where iohelper will operate on O_DIRECT fds. There, the user-space memory must be aligned to file system boundaries (at least 512, but using page-aligned works better, and some file systems prefer 64k). Made tougher by the fact that VIR_ALLOC won't work on void *, but posix_memalign won't work on char * and isn't available everywhere. This patch makes some simplifying assumptions - namely, output to an O_DIRECT fd will only be attempted on an empty seekable file (hence, no need to worry about preserving existing data on a partial block, and ftruncate will work to undo the effects of having to round up the size of the last block written), and input from an O_DIRECT fd will only be attempted on a complete seekable file with the only possible short read at EOF. * configure.ac (AC_CHECK_FUNCS_ONCE): Check for posix_memalign. * src/util/iohelper.c (runIO): Use aligned memory, and handle quirks of O_DIRECT on last write. --- v2: merge patch 6 and 15 of v1. Sorry, I didn't add a testsuite of this yet, but agree that it would be a nice project configure.ac | 6 ++-- src/util/iohelper.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++-- 2 files changed, 52 insertions(+), 6 deletions(-)