Re: [libvirt] [Xen-devel] [PATCH] libxl: fix dom0 autoballooning with Xen 4.8

Jim Fehlig wrote: > xen.git commit 57f8b13c changed several of the libxl memory > get/set functions to take 64 bit parameters. The libvirt > libxl driver still uses uint32_t variables for these various > parameters, which is particularly problematic for the > libxl_set_memory_target() function. > > When dom0 autoballooning is enabled, libvirt (like xl) determines > the memory needed to start a domain and the memory available. If > memory available is less than memory needed, dom0 is ballooned > down by passing a negative value to libxl_set_memory_target() > 'target_memkb' parameter. Prior to xen.git commit 57f8b13c, > 'target_memkb' was an int32_t. Subtracting a larger uint32 from > a smaller uint32 and assigning it to int32 resulted in a negative > number. After commit 57f8b13c, the same subtraction is widened > to a int64, resulting in a large positive number. The simple > fix taken by this patch is to assign the difference of the > uint32 values to a temporary int32 variable, which is then > passed to 'target_memkb' parameter of libxl_set_memory_target(). > > Note that it is undesirable to change libvirt to use 64 bit > variables since it requires setting LIBXL_API_VERSION to 0x040800. > Currently libvirt supports LIBXL_API_VERSION >= 0x040400, > essentially Xen >= 4.4. Any comments on this patch? xen-devel is already in cc, but I'll add Wei (one of the Xen tools maintainers) and Juergen (author of commit 57f8b13c) for some additional exposure :-). Currently, "out-of-the-box" Xen >= 4.8 + libvirt setup (dom0 autoballooning enabled) is broken without this fix. Regards, Jim > > Signed-off-by: Jim Fehlig <jfehlig(a)suse.com&gt; > --- > src/libxl/libxl_domain.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/src/libxl/libxl_domain.c b/src/libxl/libxl_domain.c > index a5314b0..ed73cd2 100644 > --- a/src/libxl/libxl_domain.c > +++ b/src/libxl/libxl_domain.c > @@ -909,6 +909,7 @@ libxlDomainFreeMem(libxl_ctx *ctx, libxl_domain_config *d_config) > { > uint32_t needed_mem; > uint32_t free_mem; > + int32_t target_mem; > int tries = 3; > int wait_secs = 10; > > @@ -922,7 +923,8 @@ libxlDomainFreeMem(libxl_ctx *ctx, libxl_domain_config *d_config) > if (free_mem >= needed_mem) > return 0; > > - if (libxl_set_memory_target(ctx, 0, free_mem - needed_mem, > + target_mem = free_mem - needed_mem; > + if (libxl_set_memory_target(ctx, 0, target_mem,

> /* relative */ 1, 0) < 0) > goto error; >