[Qemu-devel] [PATCH for-2.7 05/15] raw-posix: Implement .bdrv_lockf

[Fam Zheng <famz@redhat.com>]

Because virtlockd in libvirt already uses the fcntl lock on the image file, we
have to workaround this by locking a digest-mapped temporary file.

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 block/raw-posix.c | 97 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 97 insertions(+)

diff --git a/block/raw-posix.c b/block/raw-posix.c
index 906d5c9..277f20d 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -35,6 +35,7 @@
 #include "raw-aio.h"
 #include "qapi/util.h"
 #include "qapi/qmp/qstring.h"
+#include "glib.h"
 
 #if defined(__APPLE__) && (__MACH__)
 #include <paths.h>
@@ -149,6 +150,9 @@ typedef struct BDRVRawState {
     bool discard_zeroes:1;
     bool has_fallocate;
     bool needs_alignment;
+    bool image_locked;
+    int lock_file_fd;
+    char *lock_file_name;
 } BDRVRawState;
 
 typedef struct BDRVRawReopenState {
@@ -397,6 +401,87 @@ static void raw_attach_aio_context(BlockDriverState *bs,
 #endif
 }
 
+static int raw_do_lockf(int fd, BdrvLockfCmd cmd)
+{
+    int ret;
+    struct flock fl = (struct flock) {
+        .l_start = 0,
+        .l_whence  = SEEK_SET,
+        .l_len = 0,
+    };
+    switch (cmd) {
+    case BDRV_LOCKF_RWLOCK:
+        fl.l_type = F_WRLCK;
+        break;
+    case BDRV_LOCKF_ROLOCK:
+        fl.l_type = F_RDLCK;
+        break;
+    case BDRV_LOCKF_UNLOCK:
+        fl.l_type = F_UNLCK;
+        break;
+    default:
+        abort();
+    }
+    ret = fcntl(fd, F_SETLK, &fl);
+    return ret == -1 ? -errno : 0;
+}
+
+static char *raw_get_lock_file_name(BlockDriverState *bs)
+{
+    GChecksum *cksm;
+    const char *digest;
+    char *lock_file = NULL;
+    char *fullpath = g_malloc(PATH_MAX);
+
+    if (!realpath(bs->filename, fullpath)) {
+        pstrcpy(fullpath, PATH_MAX, bs->filename);
+    }
+    cksm = g_checksum_new(G_CHECKSUM_SHA1);
+    g_checksum_update(cksm, (const guchar *)fullpath, strlen(fullpath));
+    g_free(fullpath);
+    digest = g_checksum_get_string(cksm);
+    if (digest) {
+        lock_file = g_strdup_printf("/var/tmp/.qemu-%s.lock", digest);
+    }
+    g_checksum_free(cksm);
+    return lock_file;
+}
+
+static int raw_lockf(BlockDriverState *bs, BdrvLockfCmd cmd, Error **errp)
+{
+
+    BDRVRawState *s = bs->opaque;
+    int ret;
+
+    if ((cmd == BDRV_LOCKF_UNLOCK) == (!s->image_locked)) {
+        return 0;
+    }
+    if (s->lock_file_fd == -1) {
+        /* Create and open the lock file if necessary. */
+
+        assert(cmd != BDRV_LOCKF_UNLOCK);
+
+        s->lock_file_name = raw_get_lock_file_name(bs);
+
+        s->lock_file_fd = qemu_open(s->lock_file_name, O_RDWR | O_CREAT, 0644);
+        if (s->lock_file_fd == -1) {
+            error_setg_errno(errp, errno, "Failed to open file");
+            ret = -EIO;
+            goto out;
+        }
+    }
+
+    ret = raw_do_lockf(s->lock_file_fd, cmd);
+    if (ret) {
+        error_setg_errno(errp, errno,
+                         "Failed to lock file: %s", s->lock_file_name);
+    } else {
+        s->image_locked = cmd != BDRV_LOCKF_UNLOCK;
+    }
+out:
+    return ret;
+}
+
 #ifdef CONFIG_LINUX_AIO
 static int raw_set_aio(void **aio_ctx, int *use_aio, int bdrv_flags)
 {
@@ -585,6 +670,7 @@ static int raw_open(BlockDriverState *bs, QDict *options, int flags,
     int ret;
 
     s->type = FTYPE_FILE;
+    s->lock_file_fd = -1;
     ret = raw_open_common(bs, options, flags, 0, &local_err);
     if (local_err) {
         error_propagate(errp, local_err);
@@ -1393,6 +1479,15 @@ static void raw_close(BlockDriverState *bs)
 
     raw_detach_aio_context(bs);
 
+    if (s->lock_file_fd != -1) {
+        qemu_close(s->lock_file_fd);
+        s->lock_file_fd = -1;
+    }
+    if (s->lock_file_name) {
+        unlink(s->lock_file_name);
+        g_free(s->lock_file_name);
+        s->lock_file_name = NULL;
+   }
 #ifdef CONFIG_LINUX_AIO
     if (s->use_aio) {
         laio_cleanup(s->aio_ctx);
@@ -1960,6 +2055,8 @@ BlockDriver bdrv_file = {
     .bdrv_detach_aio_context = raw_detach_aio_context,
     .bdrv_attach_aio_context = raw_attach_aio_context,
 
+    .bdrv_lockf = raw_lockf,
+
     .create_opts = &raw_create_opts,
 };
 
-- 
2.8.0