Re: [Libguestfs] [PATCH] file: Zero support for block devices and NFS 4.2

> @@ -42,6 +43,8 @@ #include <sys/stat.h> > #include <errno.h> > #include <linux/falloc.h> /* For FALLOC_FL_* on RHEL, glibc < 2.18 */ > +#include <sys/ioctl.h> > +#include <linux/fs.h> Does this need a configure-time probe to see if it exists, since it will break compilation on BSD systems? Same question to linux/falloc.h. Actually, linux/falloc.h doesn't see any use in the current nbdkit.git; does this email depend on another thread being applied first?

+ > +#ifdef FALLOC_FL_PUNCH_HOLE > + /* If we can punch hole but may not trim, we can combine punching hole and > + fallocate to zero a range. This is much more efficient than writing zeros > + manually. */ s/is/can be/ (it's two syscalls instead of one, and may not be as efficient as we'd like - but does indeed stand a chance of being more efficient than manual efforts)

> + if (h->can_punch_hole && h->can_fallocate) { > + r = do_fallocate (h->fd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, > + offset, count); > + if (r == 0) { > + r = do_fallocate(h->fd, 0, offset, count); > + if (r == 0) > + return 0; > + > + if (errno != EOPNOTSUPP) { > + nbdkit_error ("zero: %m"); > + return r; > + } > + > + h->can_fallocate = false; > + } else { > + if (errno != EOPNOTSUPP) { > + nbdkit_error ("zero: %m"); > + return r; > + } > + > + h->can_punch_hole = false; > + } > + } > +#endif > + > + /* For block devices, we can use BLKZEROOUT. > + NOTE: count and offset must be aligned to logical block size. */ > + if (h->is_block_device) { > + uint64_t range[2] = {offset, count}; Is it worth attempting the ioctl only when you have aligned values?

+ > + r = ioctl(h->fd, BLKZEROOUT, &range); This portion of the code be conditional on whether BLKZEROOUT is defined.