[PATCH 3/4] lxc: Implement virtual /proc/cpuinfo via LXC fuse

Julio Faracco jcfaracco at gmail.com
Sun Feb 16 19:11:47 UTC 2020


This commit tries to fix a lots of issues related to LXC VCPUs. One of
them is related to /proc/cpuinfo content. If only 1 VCPU is set, LXC
containers will show all CPUs available for host. The second one is
related to CPU share, if an user set only 1 VCPU, the container/process
will use all available CPUs. (This is not the case when `cpuset`
attribute is declared. So, this commit adds a virtual cpuinfo based on
VCPU mapping and it automatic limits the CPU usage according VCPU count.

Example (now):
LXC container - 8 CPUS with 2 VCPU:
    lxc-root# stress --cpu 8

On host machine, only CPU 0 and 1 have 100% usage.

Signed-off-by: Julio Faracco <jcfaracco at gmail.com>
---
 src/lxc/lxc_cgroup.c    | 31 ++++++++++++++++
 src/lxc/lxc_container.c | 15 ++++++++
 src/lxc/lxc_fuse.c      | 78 ++++++++++++++++++++++++++++++++++++++---
 3 files changed, 120 insertions(+), 4 deletions(-)

diff --git a/src/lxc/lxc_cgroup.c b/src/lxc/lxc_cgroup.c
index 470337e675..a6c73d9d55 100644
--- a/src/lxc/lxc_cgroup.c
+++ b/src/lxc/lxc_cgroup.c
@@ -59,6 +59,34 @@ static int virLXCCgroupSetupCpuTune(virDomainDefPtr def,
 }
 
 
+static int virLXCCgroupSetupVcpuAuto(virDomainDefPtr def,
+                                     virCgroupPtr cgroup)
+{
+    size_t i;
+    int vcpumax;
+    virBuffer buffer = VIR_BUFFER_INITIALIZER;
+    virBufferPtr cpuset = &buffer;
+
+    vcpumax = virDomainDefGetVcpusMax(def);
+    for (i = 0; i < vcpumax; i++) {
+        virDomainVcpuDefPtr vcpu = virDomainDefGetVcpu(def, i);
+        /* Cgroup is smart enough to convert numbers separated
+         * by comma into ranges. Example: "0,1,2,5," -> "0-2,5".
+         * Libvirt does not need to process it here. */
+        if (vcpu)
+            virBufferAsprintf(cpuset, "%zu,", i);
+    }
+    if (virCgroupSetCpusetCpus(cgroup,
+                               virBufferCurrentContent(cpuset)) < 0) {
+        virBufferFreeAndReset(cpuset);
+        return -1;
+    }
+
+    virBufferFreeAndReset(cpuset);
+    return 0;
+}
+
+
 static int virLXCCgroupSetupCpusetTune(virDomainDefPtr def,
                                        virCgroupPtr cgroup,
                                        virBitmapPtr nodemask)
@@ -76,6 +104,9 @@ static int virLXCCgroupSetupCpusetTune(virDomainDefPtr def,
             goto cleanup;
         /* free mask to make sure we won't use it in a wrong way later */
         VIR_FREE(mask);
+    } else {
+        /* auto mode for VCPU limits */
+        virLXCCgroupSetupVcpuAuto(def, cgroup);
     }
 
     if (virDomainNumatuneGetMode(def->numa, -1, &mode) < 0 ||
diff --git a/src/lxc/lxc_container.c b/src/lxc/lxc_container.c
index 41efe43a14..1a2c97c9f4 100644
--- a/src/lxc/lxc_container.c
+++ b/src/lxc/lxc_container.c
@@ -999,6 +999,7 @@ static int lxcContainerMountProcFuse(virDomainDefPtr def,
 {
     int ret;
     char *meminfo_path = NULL;
+    char *cpuinfo_path = NULL;
 
     VIR_DEBUG("Mount /proc/meminfo stateDir=%s", stateDir);
 
@@ -1013,7 +1014,21 @@ static int lxcContainerMountProcFuse(virDomainDefPtr def,
                              meminfo_path);
     }
 
+    VIR_DEBUG("Mount /proc/cpuinfo stateDir=%s", stateDir);
+
+    cpuinfo_path = g_strdup_printf("/.oldroot/%s/%s.fuse/cpuinfo",
+                                   stateDir,
+                                   def->name);
+
+    if ((ret = mount(cpuinfo_path, "/proc/cpuinfo",
+                     NULL, MS_BIND, NULL)) < 0) {
+        virReportSystemError(errno,
+                             _("Failed to mount %s on /proc/cpuinfo"),
+                             cpuinfo_path);
+    }
+
     VIR_FREE(meminfo_path);
+    VIR_FREE(cpuinfo_path);
     return ret;
 }
 #else
diff --git a/src/lxc/lxc_fuse.c b/src/lxc/lxc_fuse.c
index 44f240a0b5..12fa69d494 100644
--- a/src/lxc/lxc_fuse.c
+++ b/src/lxc/lxc_fuse.c
@@ -37,6 +37,7 @@
 #if WITH_FUSE
 
 static const char *fuse_meminfo_path = "/meminfo";
+static const char *fuse_cpuinfo_path = "/cpuinfo";
 
 static int lxcProcGetattr(const char *path, struct stat *stbuf)
 {
@@ -54,7 +55,8 @@ static int lxcProcGetattr(const char *path, struct stat *stbuf)
     if (STREQ(path, "/")) {
         stbuf->st_mode = S_IFDIR | 0755;
         stbuf->st_nlink = 2;
-    } else if (STREQ(path, fuse_meminfo_path)) {
+    } else if (STREQ(path, fuse_meminfo_path) ||
+               STREQ(path, fuse_cpuinfo_path)) {
         if (stat(mempath, &sb) < 0) {
             res = -errno;
             goto cleanup;
@@ -90,6 +92,7 @@ static int lxcProcReaddir(const char *path, void *buf,
     filler(buf, ".", NULL, 0);
     filler(buf, "..", NULL, 0);
     filler(buf, fuse_meminfo_path + 1, NULL, 0);
+    filler(buf, fuse_cpuinfo_path + 1, NULL, 0);
 
     return 0;
 }
@@ -97,7 +100,8 @@ static int lxcProcReaddir(const char *path, void *buf,
 static int lxcProcOpen(const char *path G_GNUC_UNUSED,
                        struct fuse_file_info *fi G_GNUC_UNUSED)
 {
-    if (STRNEQ(path, fuse_meminfo_path))
+    if (STRNEQ(path, fuse_meminfo_path) &&
+        STRNEQ(path, fuse_cpuinfo_path))
         return -ENOENT;
 
     if ((fi->flags & 3) != O_RDONLY)
@@ -125,7 +129,7 @@ static int lxcProcHostRead(char *path, char *buf, size_t size, off_t offset)
 static int lxcProcReadMeminfo(char *hostpath, virDomainDefPtr def,
                               char *buf, size_t size, off_t offset)
 {
-    int res;
+    int res = -1;
     FILE *fd = NULL;
     char *line = NULL;
     size_t n;
@@ -151,7 +155,6 @@ static int lxcProcReadMeminfo(char *hostpath, virDomainDefPtr def,
         goto cleanup;
     }
 
-    res = -1;
     while (getline(&line, &n, fd) > 0) {
         char *ptr = strchr(line, ':');
         if (!ptr)
@@ -235,6 +238,70 @@ static int lxcProcReadMeminfo(char *hostpath, virDomainDefPtr def,
     return res;
 }
 
+
+static int lxcProcReadCpuinfo(char *hostpath, virDomainDefPtr def,
+                              char *buf, size_t size, off_t offset)
+{
+    int res = -1;
+    FILE *fd = NULL;
+    char *line = NULL;
+    size_t n;
+    virBuffer buffer = VIR_BUFFER_INITIALIZER;
+    virBufferPtr new_cpuinfo = &buffer;
+    size_t cpu;
+    size_t nvcpu;
+    size_t curcpu = 0;
+    bool get_proc = false;
+
+    fd = fopen(hostpath, "r");
+    if (fd == NULL) {
+        virReportSystemError(errno, _("Cannot open %s"), hostpath);
+        res = -errno;
+        goto cleanup;
+    }
+
+    /* /proc/cpuinfo does not support fseek */
+    if (offset > 0) {
+        res = 0;
+        goto cleanup;
+    }
+
+    nvcpu = virDomainDefGetVcpus(def);
+    while (getline(&line, &n, fd) > 0) {
+        if (sscanf(line, "processor\t: %zu", &cpu) == 1) {
+            virDomainVcpuDefPtr vcpu = virDomainDefGetVcpu(def, cpu);
+            /* VCPU is mapped */
+            if (vcpu) {
+                if (curcpu == nvcpu)
+                    break;
+
+                virBufferAsprintf(new_cpuinfo, "processor\t: %zu\n",
+                                  curcpu);
+                curcpu++;
+                get_proc = true;
+            } else {
+                get_proc = false;
+            }
+        } else {
+            /* It is not a processor index */
+            if (get_proc)
+                virBufferAdd(new_cpuinfo, line, -1);
+        }
+    }
+
+    res = strlen(virBufferCurrentContent(new_cpuinfo));
+    if (res > size)
+        res = size;
+    memcpy(buf, virBufferCurrentContent(new_cpuinfo), res);
+
+ cleanup:
+    VIR_FREE(line);
+    virBufferFreeAndReset(new_cpuinfo);
+    VIR_FORCE_FCLOSE(fd);
+    return res;
+}
+
+
 static int lxcProcRead(const char *path G_GNUC_UNUSED,
                        char *buf G_GNUC_UNUSED,
                        size_t size G_GNUC_UNUSED,
@@ -254,6 +321,9 @@ static int lxcProcRead(const char *path G_GNUC_UNUSED,
     if (STREQ(path, fuse_meminfo_path)) {
         if ((res = lxcProcReadMeminfo(hostpath, def, buf, size, offset)) < 0)
             res = lxcProcHostRead(hostpath, buf, size, offset);
+    } else if (STREQ(path, fuse_cpuinfo_path)) {
+        if ((res = lxcProcReadCpuinfo(hostpath, def, buf, size, offset)) < 0)
+            res = lxcProcHostRead(hostpath, buf, size, offset);
     }
 
     VIR_FREE(hostpath);
-- 
2.20.1





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