tools/libxc: Avoid generating inappropriate zero-content records

The code as written attempted to elide zero-content records, as such records
serve no purpose but come with a performance hit.  Unfortunately, in the case
where the hypervisor reported max size is non-zero, but the actual size is
zero, the record is not elided.

This previously tripped up the sanity checks in the restore side of migration,
but as the underlying reasons for eliding the records in the first place are
still valid, fix the elision logic.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
(cherry picked from commit 72efb1df629421037e2795f5529210aaa95ec72e)
(cherry picked from commit c31070f3505fb12f78d5b67498c6b1e460209c9a)

diff --git a/tools/libxc/xc_sr_save_x86_hvm.c b/tools/libxc/xc_sr_save_x86_hvm.c
index ba50a43a47af0da8406f32d1f1d37e4715dad2bf..5401bf96a9a00d0dd8b30dd8c6b0468e0ded3019 100644 (file)
--- a/tools/libxc/xc_sr_save_x86_hvm.c
+++ b/tools/libxc/xc_sr_save_x86_hvm.c
@@ -112,6 +112,10 @@ static int write_hvm_params(struct xc_sr_context *ctx)
         }
     }
 
+    /* No params? Skip this record. */
+    if ( hdr.count == 0 )
+        return 0;
+
     rc = write_split_record(ctx, &rec, entries, hdr.count * sizeof(*entries));
     if ( rc )
         PERROR("Failed to write HVM_PARAMS record");

diff --git a/tools/libxc/xc_sr_save_x86_pv.c b/tools/libxc/xc_sr_save_x86_pv.c
index f218d17bce01e2e5a0a42cb2b088a24f19e7c259..36b10583d6bc334063de479254559e70a9e7b71c 100644 (file)
--- a/tools/libxc/xc_sr_save_x86_pv.c
+++ b/tools/libxc/xc_sr_save_x86_pv.c
@@ -609,6 +609,10 @@ static int write_one_vcpu_extended(struct xc_sr_context *ctx, uint32_t id)
         return -1;
     }
 
+    /* No content? Skip the record. */
+    if ( domctl.u.ext_vcpucontext.size == 0 )
+        return 0;
+
     return write_split_record(ctx, &rec, &domctl.u.ext_vcpucontext,
                               domctl.u.ext_vcpucontext.size);
 }
@@ -664,6 +668,10 @@ static int write_one_vcpu_xsave(struct xc_sr_context *ctx, uint32_t id)
         goto err;
     }
 
+    /* No xsave state? Skip this record. */
+    if ( domctl.u.vcpuextstate.size == 0 )
+        goto out;
+
     rc = write_split_record(ctx, &rec, buffer, domctl.u.vcpuextstate.size);
     if ( rc )
         goto err;
@@ -730,6 +738,10 @@ static int write_one_vcpu_msrs(struct xc_sr_context *ctx, uint32_t id)
         goto err;
     }
 
+    /* No MSRs? Skip this record. */
+    if ( domctl.u.vcpu_msrs.msr_count == 0 )
+        goto out;
+
     rc = write_split_record(ctx, &rec, buffer,
                             domctl.u.vcpu_msrs.msr_count *
                             sizeof(xen_domctl_vcpu_msr_t));