On 02/18/2015 03:40 PM, Max Reitz wrote:
Add a refcount_order parameter to qcow2_create2(), use that value for
the image header and for calculating the size required for
preallocation.
For now, always pass 4.
This addition requires changes to the calculation of the file size for
the "full" and "falloc" preallocation modes. That in turn is a nice
opportunity to add a comment about that calculation not necessarily
being exact (and that being intentional).
Signed-off-by: Max Reitz <address@hidden>
---
block/qcow2.c | 47 ++++++++++++++++++++++++++++++++++++-----------
1 file changed, 36 insertions(+), 11 deletions(-)
@@ -2010,6 +2022,8 @@ static int qcow2_create(const char *filename, QemuOpts
*opts, Error **errp)
size_t cluster_size = DEFAULT_CLUSTER_SIZE;
PreallocMode prealloc;
int version = 3;
+ uint64_t refcount_bits = 16;
+ int refcount_order;
Error *local_err = NULL;
int ret;
@@ -2064,8 +2078,19 @@ static int qcow2_create(const char *filename, QemuOpts *opts, Error **errp)
goto finish;
}
+ if (version < 3 && refcount_bits != 16) {
+ error_setg(errp, "Different refcount widths than 16 bits require "
+ "compatibility level 1.1 or above (use compat=1.1 or "
+ "greater)");
+ ret = -EINVAL;
+ goto finish;
+ }
+
+ refcount_order = ffs(refcount_bits) - 1;
ffs() doesn't work on uint64_t (it gives the wrong answer for
0x100000000, for example); you want to use ffsll(). But ffsll() isn't
portable. But we have include/qemu/host-utils.h that gives us ctz64()
which is what we want (where ctz==ffs-1 other than for the special case
of 0). So this should be:
refcount_order = ctz64(refcount_bits);
With that change,
Reviewed-by: Eric Blake <address@hidden>