xl: free memory before building a domain

Free the needed amount of memory before proceeding with the domain
build.

Use a filelock to prevent other xl instances from conflicting during
this operation.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>

tools/examples/xl.conf

@@ -3,3 +3,6 @@
 # automatically balloon down dom0 when xen doesn't have enough free
 # memory to create a domain
 #autoballon=1
+
+# full path of the lockfile used by xl during domain creation
+#lockfile="/var/lock/xl"

tools/libxl/xl.c

@@ -34,6 +34,7 @@
 
 xentoollog_logger_stdiostream *logger;
 int autoballoon = 1;
+char *lockfile;
 
 static xentoollog_level minmsglevel = XTL_PROGRESS;
 
@@ -44,6 +45,7 @@ static void parse_global_config(const char *configfile,
     long l;
     XLU_Config *config;
     int e;
+    const char *buf;
 
     config = xlu_cfg_init(stderr, configfile);
     if (!config) {
@@ -60,6 +62,16 @@ static void parse_global_config(const char *configfile,
     if (!xlu_cfg_get_long (config, "autoballoon", &l))
         autoballoon = l;
 
+    if (!xlu_cfg_get_string (config, "lockfile", &buf))
+        lockfile = strdup(buf);
+    else {
+        e = asprintf(&lockfile, "%s/xl", (char *)libxl_lock_dir_path());
+        if (e < 0) {
+            fprintf(stderr, "asprintf memory allocation failed\n");
+            exit(1);
+        }
+    }
+
     xlu_cfg_destroy(config);
 }
  

tools/libxl/xl.h

@@ -92,5 +92,6 @@ extern xentoollog_logger_stdiostream *logger;
 
 /* global options */
 extern int autoballoon;
+extern char *lockfile;
 
 #endif /* XL_H */

tools/libxl/xl_cmdimpl.c

@@ -68,6 +68,7 @@ libxl_ctx ctx;
 /* when we operate on a domain, it is this one: */
 static uint32_t domid;
 static const char *common_domname;
+static int fd_lock = -1;
 
 
 static const char savefileheader_magic[32]=
@@ -234,6 +235,65 @@ static void find_domain(const char *p)
     common_domname = was_name ? p : libxl_domid_to_name(&ctx, domid);
 }
 
+static int acquire_lock(void)
+{
+    int rc;
+    struct flock fl;
+
+    /* lock already acquired */
+    if (fd_lock >= 0)
+        return ERROR_INVAL;
+
+    fl.l_type = F_WRLCK;
+    fl.l_whence = SEEK_SET;
+    fl.l_start = 0;
+    fl.l_len = 0;
+    fd_lock = open(lockfile, O_WRONLY|O_CREAT, S_IWUSR);
+    if (fd_lock < 0) {
+        fprintf(stderr, "cannot open the lockfile %s errno=%d\n", lockfile, errno);
+        return ERROR_FAIL;
+    }
+get_lock:
+    rc = fcntl(fd_lock, F_SETLKW, &fl);
+    if (rc < 0 && errno == EINTR)
+        goto get_lock;
+    if (rc < 0) {
+        fprintf(stderr, "cannot acquire lock %s errno=%d\n", lockfile, errno);
+        rc = ERROR_FAIL;
+    } else
+        rc = 0;
+    return rc;
+}
+
+static int release_lock(void)
+{
+    int rc;
+    struct flock fl;
+
+    /* lock not acquired */
+    if (fd_lock < 0)
+        return ERROR_INVAL;
+
+release_lock:
+    fl.l_type = F_UNLCK;
+    fl.l_whence = SEEK_SET;
+    fl.l_start = 0;
+    fl.l_len = 0;
+
+    rc = fcntl(fd_lock, F_SETLKW, &fl);
+    if (rc < 0 && errno == EINTR)
+        goto release_lock;
+    if (rc < 0) {
+        fprintf(stderr, "cannot release lock %s, errno=%d\n", lockfile, errno);
+        rc = ERROR_FAIL;
+    } else
+        rc = 0;
+    close(fd_lock);
+    fd_lock = -1;
+
+    return rc;
+}
+
 #define LOG(_f, _a...)   dolog(__FILE__, __LINE__, __func__, _f "\n", ##_a)
 
 static void dolog(const char *file, int line, const char *func, char *fmt, ...)
@@ -1213,6 +1273,48 @@ struct domain_create {
     char **migration_domname_r; /* from malloc */
 };
 
+static int freemem(libxl_domain_build_info *b_info, libxl_device_model_info *dm_info)
+{
+    int rc, retries = 3;
+    uint32_t need_memkb, free_memkb;
+
+    if (!autoballoon)
+        return 0;
+
+    rc = libxl_domain_need_memory(&ctx, b_info, dm_info, &need_memkb);
+    if (rc < 0)
+        return rc;
+
+    do {
+        rc = libxl_get_free_memory(&ctx, &free_memkb);
+        if (rc < 0)
+            return rc;
+
+        if (free_memkb >= need_memkb)
+            return 0;
+
+        rc = libxl_set_memory_target(&ctx, 0, free_memkb - need_memkb, 1, 0);
+        if (rc < 0)
+            return rc;
+
+        rc = libxl_wait_for_free_memory(&ctx, domid, need_memkb, 10);
+        if (!rc)
+            return 0;
+        else if (rc != ERROR_NOMEM)
+            return rc;
+
+        /* the memory target has been reached but the free memory is still
+         * not enough: loop over again */
+        rc = libxl_wait_for_memory_target(&ctx, 0, 1);
+        if (rc < 0)
+            return rc;
+
+        retries--;
+    } while (retries > 0);
+
+    return ERROR_NOMEM;
+}
+
 static int create_domain(struct domain_create *dom_info)
 {
     struct domain_config d_config;
@@ -1372,6 +1474,17 @@ static int create_domain(struct domain_create *dom_info)
 start:
     domid = 0;
 
+    rc = acquire_lock();
+    if (rc < 0)
+        goto error_out;
+
+    ret = freemem(&d_config.b_info, &dm_info);
+    if (ret < 0) {
+        fprintf(stderr, "failed to free memory for the domain\n");
+        ret = ERROR_FAIL;
+        goto error_out;
+    }
+
     ret = libxl_domain_make(&ctx, &d_config.c_info, &domid);
     if (ret) {
         fprintf(stderr, "cannot make domain: %d\n", ret);
@@ -1482,6 +1595,8 @@ start:
             goto error_out;
     }
 
+    release_lock();
+
     if (!paused)
         libxl_domain_unpause(&ctx, domid);
 
@@ -1619,6 +1734,7 @@ start:
     }
 
 error_out:
+    release_lock();
     if (domid)
         libxl_domain_destroy(&ctx, domid, 0);