[xen stable-4.8] tools/libxc: Avoid generating inappropriate zero-content records

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[xen stable-4.8] tools/libxc: Avoid generating inappropriate zero-content records

patchbot
commit c31070f3505fb12f78d5b67498c6b1e460209c9a
Author:     Andrew Cooper <[hidden email]>
AuthorDate: Thu Mar 30 17:32:32 2017 +0100
Commit:     Ian Jackson <[hidden email]>
CommitDate: Tue Feb 27 15:59:03 2018 +0000

    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 <[hidden email]>
    Reviewed-by: Wei Liu <[hidden email]>
    (cherry picked from commit 72efb1df629421037e2795f5529210aaa95ec72e)
---
 tools/libxc/xc_sr_save_x86_hvm.c |  4 ++++
 tools/libxc/xc_sr_save_x86_pv.c  | 12 ++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/tools/libxc/xc_sr_save_x86_hvm.c b/tools/libxc/xc_sr_save_x86_hvm.c
index ba50a43..5401bf9 100644
--- 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 f218d17..36b1058 100644
--- 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));
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.8

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