qemu: Use predictable file names for memory-backend-file

In some cases management application needs to allocate memory for
qemu upfront and then just let qemu use that. Since we don't want
to expose path for memory-backend-file anywhere in the domain
XML, we can generate predictable paths. In this case:

  $memoryBackingDir/libvirt/qemu/$shortName/$alias

where $shortName is result of virDomainDefGetShortName().

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: John Ferlan <jferlan@redhat.com>

src/qemu/qemu_command.c

@@ -3383,7 +3383,7 @@ qemuBuildMemoryBackendStr(virJSONValuePtr *backendProps,
         } else {
             /* We can have both pagesize and mem source. If that's the case,
              * prefer hugepages as those are more specific. */
-            if (qemuGetMemoryBackingPath(cfg, &memPath) < 0)
+            if (qemuGetMemoryBackingPath(def, cfg, mem->info.alias, &memPath) < 0)
                 goto cleanup;
         }
 

src/qemu/qemu_conf.c

@@ -1750,9 +1750,41 @@ qemuGetDomainHupageMemPath(const virDomainDef *def,
 }
 
 
+int
+qemuGetMemoryBackingBasePath(virQEMUDriverConfigPtr cfg,
+                             char **path)
+{
+    return virAsprintf(path, "%s/libvirt/qemu", cfg->memoryBackingDir);
+}
+
+
+int
+qemuGetMemoryBackingDomainPath(const virDomainDef *def,
+                               virQEMUDriverConfigPtr cfg,
+                               char **path)
+{
+    char *shortName = NULL;
+    char *base = NULL;
+    int ret = -1;
+
+    if (!(shortName = virDomainDefGetShortName(def)) ||
+        qemuGetMemoryBackingBasePath(cfg, &base) < 0 ||
+        virAsprintf(path, "%s/%s", base, shortName) < 0)
+        goto cleanup;
+
+    ret = 0;
+ cleanup:
+    VIR_FREE(base);
+    VIR_FREE(shortName);
+    return ret;
+}
+
+
 /**
  * qemuGetMemoryBackingPath:
+ * @def: domain definition
  * @cfg: the driver config
+ * @alias: memory object alias
  * @memPath: constructed path
  *
  * Constructs path to memory backing dir and stores it at @memPath.
@@ -1761,8 +1793,27 @@ qemuGetDomainHupageMemPath(const virDomainDef *def,
  *          -1 otherwise (with error reported).
  */
 int
-qemuGetMemoryBackingPath(virQEMUDriverConfigPtr cfg,
+qemuGetMemoryBackingPath(const virDomainDef *def,
+                         virQEMUDriverConfigPtr cfg,
+                         const char *alias,
                          char **memPath)
 {
-    return VIR_STRDUP(*memPath, cfg->memoryBackingDir);
+    char *domainPath = NULL;
+    int ret = -1;
+
+    if (!alias) {
+        /* This should never happen (TM) */
+        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                       _("memory device alias is not assigned"));
+        goto cleanup;
+    }
+
+    if (qemuGetMemoryBackingDomainPath(def, cfg, &domainPath) < 0 ||
+        virAsprintf(memPath, "%s/%s", domainPath, alias) < 0)
+        goto cleanup;
+
+    ret = 0;
+ cleanup:
+    VIR_FREE(domainPath);
+    return ret;
 }

src/qemu/qemu_conf.h

@@ -364,6 +364,13 @@ int qemuGetDomainHupageMemPath(const virDomainDef *def,
                                unsigned long long pagesize,
                                char **memPath);
 
-int qemuGetMemoryBackingPath(virQEMUDriverConfigPtr cfg,
+int qemuGetMemoryBackingBasePath(virQEMUDriverConfigPtr cfg,
+                                 char **path);
+int qemuGetMemoryBackingDomainPath(const virDomainDef *def,
+                                   virQEMUDriverConfigPtr cfg,
+                                   char **path);
+int qemuGetMemoryBackingPath(const virDomainDef *def,
+                             virQEMUDriverConfigPtr cfg,
+                             const char *alias,
                              char **memPath);
 #endif /* __QEMUD_CONF_H */

src/qemu/qemu_driver.c

@@ -631,6 +631,7 @@ qemuStateInitialize(bool privileged,
     uid_t run_uid = -1;
     gid_t run_gid = -1;
     char *hugepagePath = NULL;
+    char *memoryBackingPath = NULL;
     size_t i;
 
     if (VIR_ALLOC(qemu_driver) < 0)
@@ -889,6 +890,21 @@ qemuStateInitialize(bool privileged,
         VIR_FREE(hugepagePath);
     }
 
+    if (qemuGetMemoryBackingBasePath(cfg, &memoryBackingPath) < 0)
+        goto error;
+
+    if (virFileMakePath(memoryBackingPath) < 0) {
+        virReportSystemError(errno,
+                             _("unable to create memory backing path %s"),
+                             memoryBackingPath);
+        goto error;
+    }
+
+    if (privileged &&
+        virFileUpdatePerm(memoryBackingPath,
+                          0, S_IXGRP | S_IXOTH) < 0)
+        goto error;
+
     if (!(qemu_driver->closeCallbacks = virCloseCallbacksNew()))
         goto error;
 
@@ -946,6 +962,7 @@ qemuStateInitialize(bool privileged,
     virObjectUnref(conn);
     VIR_FREE(driverConf);
     VIR_FREE(hugepagePath);
+    VIR_FREE(memoryBackingPath);
     qemuStateCleanup();
     return -1;
 }

src/qemu/qemu_process.c

@@ -3324,6 +3324,36 @@ qemuProcessNeedHugepagesPath(virDomainDefPtr def,
 }
 
 
+static bool
+qemuProcessNeedMemoryBackingPath(virDomainDefPtr def,
+                                 virDomainMemoryDefPtr mem)
+{
+    size_t i;
+    size_t numaNodes;
+
+    if (def->mem.source == VIR_DOMAIN_MEMORY_SOURCE_FILE ||
+        def->mem.access != VIR_DOMAIN_MEMORY_ACCESS_DEFAULT)
+        return true;
+
+    numaNodes = virDomainNumaGetNodeCount(def->numa);
+    for (i = 0; i < numaNodes; i++) {
+        if (virDomainNumaGetNodeMemoryAccessMode(def->numa, i)
+            != VIR_DOMAIN_MEMORY_ACCESS_DEFAULT)
+            return true;
+    }
+
+    if (mem &&
+        mem->model == VIR_DOMAIN_MEMORY_MODEL_DIMM &&
+        (mem->access != VIR_DOMAIN_MEMORY_ACCESS_DEFAULT ||
+         (mem->targetNode >= 0 &&
+          virDomainNumaGetNodeMemoryAccessMode(def->numa, mem->targetNode)
+          != VIR_DOMAIN_MEMORY_ACCESS_DEFAULT)))
+        return true;
+
+    return false;
+}
+
+
 static int
 qemuProcessBuildDestroyMemoryPathsImpl(virQEMUDriverPtr driver,
                                        virDomainDefPtr def,
@@ -3363,33 +3393,46 @@ qemuProcessBuildDestroyMemoryPaths(virQEMUDriverPtr driver,
                                    bool build)
 {
     virQEMUDriverConfigPtr cfg = virQEMUDriverGetConfig(driver);
-    char *hugepagePath = NULL;
+    char *path = NULL;
     size_t i;
-    bool shouldBuild = false;
+    bool shouldBuildHP = false;
+    bool shouldBuildMB = false;
     int ret = -1;
 
-    if (build)
+    if (build) {
-        shouldBuild = qemuProcessNeedHugepagesPath(vm->def, mem);
+        shouldBuildHP = qemuProcessNeedHugepagesPath(vm->def, mem);
+        shouldBuildMB = qemuProcessNeedMemoryBackingPath(vm->def, mem);
+    }
 
-    if (!build || shouldBuild) {
+    if (!build || shouldBuildHP) {
         for (i = 0; i < cfg->nhugetlbfs; i++) {
-            VIR_FREE(hugepagePath);
+            path = qemuGetDomainHugepagePath(vm->def, &cfg->hugetlbfs[i]);
-            hugepagePath = qemuGetDomainHugepagePath(vm->def, &cfg->hugetlbfs[i]);
 
-            if (!hugepagePath)
+            if (!path)
                 goto cleanup;
 
             if (qemuProcessBuildDestroyMemoryPathsImpl(driver, vm->def,
-                                                       hugepagePath, build) < 0)
+                                                       path, build) < 0)
                 goto cleanup;
 
-            VIR_FREE(hugepagePath);
+            VIR_FREE(path);
         }
     }
 
+    if (!build || shouldBuildMB) {
+        if (qemuGetMemoryBackingDomainPath(vm->def, cfg, &path) < 0)
+            goto cleanup;
+
+        if (qemuProcessBuildDestroyMemoryPathsImpl(driver, vm->def,
+                                                   path, build) < 0)
+            goto cleanup;
+
+        VIR_FREE(path);
+    }
+
     ret = 0;
  cleanup:
-    VIR_FREE(hugepagePath);
+    VIR_FREE(path);
     virObjectUnref(cfg);
     return ret;
 }

tests/qemuxml2argvdata/qemuxml2argv-cpu-numa-memshared.args

@@ -10,10 +10,12 @@ QEMU_AUDIO_DRV=none \
 -M pc \
 -m 214 \
 -smp 16,sockets=2,cores=4,threads=2 \
--object memory-backend-file,id=ram-node0,mem-path=/var/lib/libvirt/qemu/ram,\
+-object memory-backend-file,id=ram-node0,\
+mem-path=/var/lib/libvirt/qemu/ram/libvirt/qemu/-1-QEMUGuest1/ram-node0,\
 share=yes,size=112197632 \
 -numa node,nodeid=0,cpus=0-7,memdev=ram-node0 \
--object memory-backend-file,id=ram-node1,mem-path=/var/lib/libvirt/qemu/ram,\
+-object memory-backend-file,id=ram-node1,\
+mem-path=/var/lib/libvirt/qemu/ram/libvirt/qemu/-1-QEMUGuest1/ram-node1,\
 share=no,size=112197632 \
 -numa node,nodeid=1,cpus=8-15,memdev=ram-node1 \
 -uuid c7a5fdbd-edaf-9455-926a-d65c16db1809 \

tests/qemuxml2argvdata/qemuxml2argv-fd-memory-numa-topology.args

@@ -11,7 +11,8 @@ QEMU_AUDIO_DRV=none \
 -m 14336 \
 -mem-prealloc \
 -smp 8,sockets=1,cores=8,threads=1 \
--object memory-backend-file,id=ram-node0,mem-path=/var/lib/libvirt/qemu/ram,\
+-object memory-backend-file,id=ram-node0,\
+mem-path=/var/lib/libvirt/qemu/ram/libvirt/qemu/-1-instance-00000092/ram-node0,\
 share=yes,size=15032385536 \
 -numa node,nodeid=0,cpus=0-7,memdev=ram-node0 \
 -uuid 126f2720-6f8e-45ab-a886-ec9277079a67 \

tests/qemuxml2argvdata/qemuxml2argv-fd-memory-numa-topology2.args

@@ -11,10 +11,12 @@ QEMU_AUDIO_DRV=none \
 -m 28672 \
 -mem-prealloc \
 -smp 20,sockets=1,cores=8,threads=1 \
--object memory-backend-file,id=ram-node0,mem-path=/var/lib/libvirt/qemu/ram,\
+-object memory-backend-file,id=ram-node0,\
+mem-path=/var/lib/libvirt/qemu/ram/libvirt/qemu/-1-instance-00000092/ram-node0,\
 share=no,size=15032385536 \
 -numa node,nodeid=0,cpus=0-7,memdev=ram-node0 \
--object memory-backend-file,id=ram-node1,mem-path=/var/lib/libvirt/qemu/ram,\
+-object memory-backend-file,id=ram-node1,\
+mem-path=/var/lib/libvirt/qemu/ram/libvirt/qemu/-1-instance-00000092/ram-node1,\
 share=yes,size=15032385536 \
 -numa node,nodeid=1,cpus=8-15,memdev=ram-node1 \
 -uuid 126f2720-6f8e-45ab-a886-ec9277079a67 \

tests/qemuxml2argvdata/qemuxml2argv-fd-memory-numa-topology3.args

@@ -11,13 +11,16 @@ QEMU_AUDIO_DRV=none \
 -m 43008 \
 -mem-prealloc \
 -smp 32,sockets=1,cores=24,threads=1 \
--object memory-backend-file,id=ram-node0,mem-path=/var/lib/libvirt/qemu/ram,\
+-object memory-backend-file,id=ram-node0,\
+mem-path=/var/lib/libvirt/qemu/ram/libvirt/qemu/-1-instance-00000092/ram-node0,\
 share=yes,size=15032385536 \
 -numa node,nodeid=0,cpus=0-1,memdev=ram-node0 \
--object memory-backend-file,id=ram-node1,mem-path=/var/lib/libvirt/qemu/ram,\
+-object memory-backend-file,id=ram-node1,\
+mem-path=/var/lib/libvirt/qemu/ram/libvirt/qemu/-1-instance-00000092/ram-node1,\
 share=yes,size=15032385536 \
 -numa node,nodeid=1,cpus=2-3,memdev=ram-node1 \
--object memory-backend-file,id=ram-node2,mem-path=/var/lib/libvirt/qemu/ram,\
+-object memory-backend-file,id=ram-node2,\
+mem-path=/var/lib/libvirt/qemu/ram/libvirt/qemu/-1-instance-00000092/ram-node2,\
 share=no,size=15032385536 \
 -numa node,nodeid=2,cpus=4-5,memdev=ram-node2 \
 -uuid 126f2720-6f8e-45ab-a886-ec9277079a67 \

tests/qemuxml2argvdata/qemuxml2argv-hugepages-memaccess2.args

@@ -10,17 +10,20 @@ QEMU_AUDIO_DRV=none \
 -M pc \
 -m size=4194304k,slots=16,maxmem=8388608k \
 -smp 4,sockets=4,cores=1,threads=1 \
--object memory-backend-file,id=ram-node0,mem-path=/var/lib/libvirt/qemu/ram,\
+-object memory-backend-file,id=ram-node0,\
+mem-path=/var/lib/libvirt/qemu/ram/libvirt/qemu/-1-QEMUGuest1/ram-node0,\
 share=no,size=1073741824,host-nodes=0-3,policy=bind \
 -numa node,nodeid=0,cpus=0,memdev=ram-node0 \
 -object memory-backend-file,id=ram-node1,prealloc=yes,\
 mem-path=/dev/hugepages2M/libvirt/qemu/-1-QEMUGuest1,share=yes,size=1073741824,\
 host-nodes=0-3,policy=bind \
 -numa node,nodeid=1,cpus=1,memdev=ram-node1 \
--object memory-backend-file,id=ram-node2,mem-path=/var/lib/libvirt/qemu/ram,\
+-object memory-backend-file,id=ram-node2,\
+mem-path=/var/lib/libvirt/qemu/ram/libvirt/qemu/-1-QEMUGuest1/ram-node2,\
 share=no,size=1073741824,host-nodes=0-3,policy=bind \
 -numa node,nodeid=2,cpus=2,memdev=ram-node2 \
--object memory-backend-file,id=ram-node3,mem-path=/var/lib/libvirt/qemu/ram,\
+-object memory-backend-file,id=ram-node3,\
+mem-path=/var/lib/libvirt/qemu/ram/libvirt/qemu/-1-QEMUGuest1/ram-node3,\
 share=no,size=1073741824,host-nodes=3,policy=bind \
 -numa node,nodeid=3,cpus=3,memdev=ram-node3 \
 -object memory-backend-file,id=memdimm0,prealloc=yes,\