qemu-kvm/SOURCES/kvm-block-blkio-use-qemu_open-to-support-fd-passing-for-.patch

From fd57241cf0f8c2906fa56118f8da1e65a5b1e4d8 Mon Sep 17 00:00:00 2001
From: Stefano Garzarella <sgarzare@redhat.com>
Date: Tue, 30 May 2023 09:19:40 +0200
Subject: [PATCH 3/5] block/blkio: use qemu_open() to support fd passing for
 virtio-blk

RH-Author: Stefano Garzarella <sgarzare@redhat.com>
RH-MergeRequest: 169: block/blkio: support fd passing for virtio-blk-vhost-vdpa driver
RH-Bugzilla: 2180076
RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>
RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
RH-Commit: [1/2] 9ff1a1510500db101648341207a36318a0c41c5a (sgarzarella/qemu-kvm-c-9-s)

Some virtio-blk drivers (e.g. virtio-blk-vhost-vdpa) supports the fd
passing. Let's expose this to the user, so the management layer
can pass the file descriptor of an already opened path.

If the libblkio virtio-blk driver supports fd passing, let's always
use qemu_open() to open the `path`, so we can handle fd passing
from the management layer through the "/dev/fdset/N" special path.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Message-id: 20230530071941.8954-2-sgarzare@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
(cherry picked from commit cad2ccc395c7113fb30bc9390774b67b34f06c68)
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
 block/blkio.c | 53 ++++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 44 insertions(+), 9 deletions(-)

diff --git a/block/blkio.c b/block/blkio.c
index 0cdc99a729..6a6f20f923 100644
--- a/block/blkio.c
+++ b/block/blkio.c
@@ -672,25 +672,60 @@ static int blkio_virtio_blk_common_open(BlockDriverState *bs,
 {
     const char *path = qdict_get_try_str(options, "path");
     BDRVBlkioState *s = bs->opaque;
-    int ret;
+    bool fd_supported = false;
+    int fd, ret;
 
     if (!path) {
         error_setg(errp, "missing 'path' option");
         return -EINVAL;
     }
 
-    ret = blkio_set_str(s->blkio, "path", path);
-    qdict_del(options, "path");
-    if (ret < 0) {
-        error_setg_errno(errp, -ret, "failed to set path: %s",
-                         blkio_get_error_msg());
-        return ret;
-    }
-
     if (!(flags & BDRV_O_NOCACHE)) {
         error_setg(errp, "cache.direct=off is not supported");
         return -EINVAL;
     }
+
+    if (blkio_get_int(s->blkio, "fd", &fd) == 0) {
+        fd_supported = true;
+    }
+
+    /*
+     * If the libblkio driver supports fd passing, let's always use qemu_open()
+     * to open the `path`, so we can handle fd passing from the management
+     * layer through the "/dev/fdset/N" special path.
+     */
+    if (fd_supported) {
+        int open_flags;
+
+        if (flags & BDRV_O_RDWR) {
+            open_flags = O_RDWR;
+        } else {
+            open_flags = O_RDONLY;
+        }
+
+        fd = qemu_open(path, open_flags, errp);
+        if (fd < 0) {
+            return -EINVAL;
+        }
+
+        ret = blkio_set_int(s->blkio, "fd", fd);
+        if (ret < 0) {
+            error_setg_errno(errp, -ret, "failed to set fd: %s",
+                             blkio_get_error_msg());
+            qemu_close(fd);
+            return ret;
+        }
+    } else {
+        ret = blkio_set_str(s->blkio, "path", path);
+        if (ret < 0) {
+            error_setg_errno(errp, -ret, "failed to set path: %s",
+                             blkio_get_error_msg());
+            return ret;
+        }
+    }
+
+    qdict_del(options, "path");
+
     return 0;
 }
 
-- 
2.39.3