Christoph Hellwig wrote:
What use is there geeting the extent count for a range? I'd rather do it only per-file like the xfs ioctl.
I'll answer that from practical experience. Our api equivalents: __u64 fm_start; /* logical offset (inclusive) at * which to start mapping (in) */ __u64 fm_length; /* logical length of mapping which * userspace cares about (in) */ __u32 fm_extent_count; /* size of fm_extents array (in) */ __u32 fm_mapped_extents; /* number of extents that were * mapped (out) */ ... note it has no flags field and no separate ioctl_extent_count. "fm_extent_count" is IN == max_extents to return. OUT == number of extents remaining in-range after fm_mapped_extents Pass in fm_extent_count==0 and you get OUT number of extent entries within your fm_start + fm_length range. Which you can use to set your malloc size because the FS can have massive extent counts :( This is why it was done. In practice this was only used by kernel callers because most application developers simply looped with a fixed buffer and adjusted fm_start. Dumber applications kept doubling their malloc to get all extents at once... or core dump :) I'm not saying there is a good reason to do it this way in linux, just why someone else did it that way. jim -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
