[libvirt] [PATCH 4/7] Add a helper API for setting up a NBD device with qemu-nbd

[Daniel P. Berrange]

From: "Daniel P. Berrange" <berrange at redhat.com>

Add a virFileNBDDeviceAssociate method, which given a filename
will setup a NBD device, using qemu-nbd as the server.

Signed-off-by: Daniel P. Berrange <berrange at redhat.com>
---
 src/libvirt_private.syms |   1 +
 src/util/virfile.c       | 124 +++++++++++++++++++++++++++++++++++++++++++++++
 src/util/virfile.h       |   4 ++
 3 files changed, 129 insertions(+)

diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index 5cad990..0607bae 100644
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -1253,6 +1253,7 @@ virFileDirectFdFlag;
 virFileFclose;
 virFileFdopen;
 virFileLoopDeviceAssociate;
+virFileNBDDeviceAssociate;
 virFileRewrite;
 virFileTouch;
 virFileUpdatePerm;
diff --git a/src/util/virfile.c b/src/util/virfile.c
index 4a9fa81..095559e 100644
--- a/src/util/virfile.c
+++ b/src/util/virfile.c
@@ -631,6 +631,119 @@ cleanup:
     return lofd;
 }
 
+
+# define SYSFS_BLOCK_DIR "/sys/block"
+
+
+static int
+virFileNBDDeviceIsBusy(const char *devname)
+{
+    char *path;
+    int ret = -1;
+
+    if (virAsprintf(&path, SYSFS_BLOCK_DIR "/%s/pid",
+                    devname) < 0) {
+        virReportOOMError();
+        return -1;
+    }
+
+    if (access(path, F_OK) < 0) {
+        if (errno == ENOENT)
+            ret = 0;
+        else
+            virReportSystemError(errno,
+                                 _("Cannot check NBD device %s pid"),
+                                 devname);
+        goto cleanup;
+    }
+    ret = 1;
+
+cleanup:
+    VIR_FREE(path);
+    return ret;
+}
+
+
+static char *
+virFileNBDDeviceFindUnused(void)
+{
+    DIR *dh;
+    char *ret = NULL;
+    struct dirent *de;
+
+    if (!(dh = opendir(SYSFS_BLOCK_DIR))) {
+        virReportSystemError(errno,
+                             _("Cannot read directory %s"),
+                             SYSFS_BLOCK_DIR);
+        return NULL;
+    }
+
+    while ((de = readdir(dh)) != NULL) {
+        if (STRPREFIX(de->d_name, "nbd")) {
+            int rv = virFileNBDDeviceIsBusy(de->d_name);
+            if (rv < 0)
+                goto cleanup;
+            if (rv == 0) {
+                if (virAsprintf(&ret, "/dev/%s", de->d_name) < 0) {
+                    virReportOOMError();
+                    goto cleanup;
+                }
+                goto cleanup;
+            }
+        }
+    }
+
+    virReportSystemError(EBUSY, "%s",
+                         _("No free NBD devices"));
+
+cleanup:
+    closedir(dh);
+    return ret;
+}
+
+
+int virFileNBDDeviceAssociate(const char *file,
+                              char **dev,
+                              bool readonly)
+{
+    char *nbddev;
+    char *qemunbd;
+    virCommandPtr cmd = NULL;
+    int ret = -1;
+
+    if (!(nbddev = virFileNBDDeviceFindUnused()))
+        goto cleanup;
+
+    if (!(qemunbd = virFindFileInPath("qemu-nbd"))) {
+        virReportSystemError(ENOENT, "%s",
+                             _("Unable to find 'qemu-nbd' binary in $PATH"));
+        goto cleanup;
+    }
+
+    cmd = virCommandNew(qemunbd);
+    if (readonly)
+        virCommandAddArg(cmd, "-r");
+    virCommandAddArgList(cmd,
+                         "-n", /* Don't cache in qemu-nbd layer */
+                         "-c", nbddev,
+                         file, NULL);
+
+    /* qemu-nbd will daemonize itself */
+
+    if (virCommandRun(cmd, NULL) < 0)
+        goto cleanup;
+
+    *dev = nbddev;
+    nbddev = NULL;
+    ret = 0;
+
+cleanup:
+    VIR_FREE(nbddev);
+    VIR_FREE(qemunbd);
+    virCommandFree(cmd);
+    return ret;
+}
+
 #else /* __linux__ */
 
 int virFileLoopDeviceAssociate(const char *file,
@@ -643,4 +756,15 @@ int virFileLoopDeviceAssociate(const char *file,
     return -1;
 }
 
+int virFileNBDDeviceAssociate(const char *file,
+                              char **dev ATTRIBUTE_UNUSED,
+                              bool readonly ATTRIBUTE_UNUSED)
+{
+    virReportSystemError(ENOSYS,
+                         _("Unable to associate file %s with NBD device"),
+                         file);
+    *dev = NULL;
+    return -1;
+}
+
 #endif /* __linux__ */
diff --git a/src/util/virfile.h b/src/util/virfile.h
index c885b73..6c9179b 100644
--- a/src/util/virfile.h
+++ b/src/util/virfile.h
@@ -108,4 +108,8 @@ int virFileUpdatePerm(const char *path,
 int virFileLoopDeviceAssociate(const char *file,
                                char **dev);
 
+int virFileNBDDeviceAssociate(const char *file,
+                              char **dev,
+                              bool readonly);
+
 #endif /* __VIR_FILES_H */
-- 
1.7.11.7