block: Separate blk_is_writable() and blk_supports_write_perm()

Currently, blk_is_read_only() tells whether a given BlockBackend can
only be used in read-only mode because its root node is read-only. Some
callers actually try to answer a slightly different question: Is the
BlockBackend configured to be writable, by taking write permissions on
the root node?

This can differ, for example, for CD-ROM devices which don't take write
permissions, but may be backed by a writable image file. scsi-cd allows
write requests to the drive if blk_is_read_only() returns false.
However, the write request will immediately run into an assertion
failure because the write permission is missing.

This patch introduces separate functions for both questions.
blk_supports_write_perm() answers the question whether the block
node/image file can support writable devices, whereas blk_is_writable()
tells whether the BlockBackend is currently configured to be writable.

All calls of blk_is_read_only() are converted to one of the two new
functions.

Fixes: https://bugs.launchpad.net/bugs/1906693
Cc: qemu-stable@nongnu.org
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20210118123448.307825-2-kwolf@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

11 files changed, 24 insertions, 22 deletions

diff --git a/hw/block/dataplane/xen-block.c b/hw/block/dataplane/xen-block.c
index 3675f8deaf..860787580a 100644
--- a/hw/block/dataplane/xen-block.c
+++ b/hw/block/dataplane/xen-block.c
@@ -168,7 +168,7 @@ static int xen_block_parse_request(XenBlockRequest *request)
     };
 
     if (request->req.operation != BLKIF_OP_READ &&
-        blk_is_read_only(dataplane->blk)) {
+        !blk_is_writable(dataplane->blk)) {
         error_report("error: write req for ro device");
         goto err;
     }
diff --git a/hw/block/fdc.c b/hw/block/fdc.c
index 3636874432..292ea87805 100644
--- a/hw/block/fdc.c
+++ b/hw/block/fdc.c
@@ -444,7 +444,7 @@ static void fd_revalidate(FDrive *drv)
 
     FLOPPY_DPRINTF("revalidate\n");
     if (drv->blk != NULL) {
-        drv->ro = blk_is_read_only(drv->blk);
+        drv->ro = !blk_is_writable(drv->blk);
         if (!blk_is_inserted(drv->blk)) {
             FLOPPY_DPRINTF("No disk in drive\n");
             drv->disk = FLOPPY_DRIVE_TYPE_NONE;
@@ -479,8 +479,8 @@ static void fd_change_cb(void *opaque, bool load, Error **errp)
         blk_set_perm(drive->blk, 0, BLK_PERM_ALL, &error_abort);
     } else {
         if (!blkconf_apply_backend_options(drive->conf,
-                                           blk_is_read_only(drive->blk), false,
-                                           errp)) {
+                                           !blk_supports_write_perm(drive->blk),
+                                           false, errp)) {
             return;
         }
     }
@@ -553,7 +553,8 @@ static void floppy_drive_realize(DeviceState *qdev, Error **errp)
          * read-only node later */
         read_only = true;
     } else {
-        read_only = !blk_bs(dev->conf.blk) || blk_is_read_only(dev->conf.blk);
+        read_only = !blk_bs(dev->conf.blk) ||
+                    !blk_supports_write_perm(dev->conf.blk);
     }
 
     if (!blkconf_blocksizes(&dev->conf, errp)) {
diff --git a/hw/block/m25p80.c b/hw/block/m25p80.c
index b744a58d1c..0412d3e7f4 100644
--- a/hw/block/m25p80.c
+++ b/hw/block/m25p80.c
@@ -508,7 +508,7 @@ static void flash_sync_page(Flash *s, int page)
 {
     QEMUIOVector *iov;
 
-    if (!s->blk || blk_is_read_only(s->blk)) {
+    if (!s->blk || !blk_is_writable(s->blk)) {
         return;
     }
 
@@ -524,7 +524,7 @@ static inline void flash_sync_area(Flash *s, int64_t off, int64_t len)
 {
     QEMUIOVector *iov;
 
-    if (!s->blk || blk_is_read_only(s->blk)) {
+    if (!s->blk || !blk_is_writable(s->blk)) {
         return;
     }
 
@@ -1434,7 +1434,7 @@ static void m25p80_realize(SSIPeripheral *ss, Error **errp)
 
     if (s->blk) {
         uint64_t perm = BLK_PERM_CONSISTENT_READ |
-                        (blk_is_read_only(s->blk) ? 0 : BLK_PERM_WRITE);
+                        (blk_supports_write_perm(s->blk) ? BLK_PERM_WRITE : 0);
         ret = blk_set_perm(s->blk, perm, BLK_PERM_ALL, errp);
         if (ret < 0) {
             return;
diff --git a/hw/block/nand.c b/hw/block/nand.c
index 913292ad1d..8bc80e3514 100644
--- a/hw/block/nand.c
+++ b/hw/block/nand.c
@@ -400,7 +400,7 @@ static void nand_realize(DeviceState *dev, Error **errp)
     pagesize = 1 << s->oob_shift;
     s->mem_oob = 1;
     if (s->blk) {
-        if (blk_is_read_only(s->blk)) {
+        if (!blk_supports_write_perm(s->blk)) {
             error_setg(errp, "Can't use a read-only drive");
             return;
         }
diff --git a/hw/block/nvme-ns.c b/hw/block/nvme-ns.c
index 31c80cdf5b..2670787d26 100644
--- a/hw/block/nvme-ns.c
+++ b/hw/block/nvme-ns.c
@@ -48,13 +48,14 @@ static void nvme_ns_init(NvmeNamespace *ns)
 
 static int nvme_ns_init_blk(NvmeCtrl *n, NvmeNamespace *ns, Error **errp)
 {
+    bool read_only;
+
     if (!blkconf_blocksizes(&ns->blkconf, errp)) {
         return -1;
     }
 
-    if (!blkconf_apply_backend_options(&ns->blkconf,
-                                       blk_is_read_only(ns->blkconf.blk),
-                                       false, errp)) {
+    read_only = !blk_supports_write_perm(ns->blkconf.blk);
+    if (!blkconf_apply_backend_options(&ns->blkconf, read_only, false, errp)) {
         return -1;
     }
 
diff --git a/hw/block/onenand.c b/hw/block/onenand.c
index 579a73d7f7..afc0cd3a0f 100644
--- a/hw/block/onenand.c
+++ b/hw/block/onenand.c
@@ -797,7 +797,7 @@ static void onenand_realize(DeviceState *dev, Error **errp)
         s->image = memset(g_malloc(size + (size >> 5)),
                           0xff, size + (size >> 5));
     } else {
-        if (blk_is_read_only(s->blk)) {
+        if (!blk_supports_write_perm(s->blk)) {
             error_setg(errp, "Can't use a read-only drive");
             return;
         }
diff --git a/hw/block/pflash_cfi01.c b/hw/block/pflash_cfi01.c
index ccf326793d..22287a1522 100644
--- a/hw/block/pflash_cfi01.c
+++ b/hw/block/pflash_cfi01.c
@@ -745,7 +745,7 @@ static void pflash_cfi01_realize(DeviceState *dev, Error **errp)
 
     if (pfl->blk) {
         uint64_t perm;
-        pfl->ro = blk_is_read_only(pfl->blk);
+        pfl->ro = !blk_supports_write_perm(pfl->blk);
         perm = BLK_PERM_CONSISTENT_READ | (pfl->ro ? 0 : BLK_PERM_WRITE);
         ret = blk_set_perm(pfl->blk, perm, BLK_PERM_ALL, errp);
         if (ret < 0) {
diff --git a/hw/block/pflash_cfi02.c b/hw/block/pflash_cfi02.c
index 2ad2f6baea..7962cff745 100644
--- a/hw/block/pflash_cfi02.c
+++ b/hw/block/pflash_cfi02.c
@@ -802,7 +802,7 @@ static void pflash_cfi02_realize(DeviceState *dev, Error **errp)
 
     if (pfl->blk) {
         uint64_t perm;
-        pfl->ro = blk_is_read_only(pfl->blk);
+        pfl->ro = !blk_supports_write_perm(pfl->blk);
         perm = BLK_PERM_CONSISTENT_READ | (pfl->ro ? 0 : BLK_PERM_WRITE);
         ret = blk_set_perm(pfl->blk, perm, BLK_PERM_ALL, errp);
         if (ret < 0) {
diff --git a/hw/block/swim.c b/hw/block/swim.c
index 20133a814c..509c2f4900 100644
--- a/hw/block/swim.c
+++ b/hw/block/swim.c
@@ -137,8 +137,8 @@ static void swim_change_cb(void *opaque, bool load, Error **errp)
         blk_set_perm(drive->blk, 0, BLK_PERM_ALL, &error_abort);
     } else {
         if (!blkconf_apply_backend_options(drive->conf,
-                                           blk_is_read_only(drive->blk), false,
-                                           errp)) {
+                                           !blk_supports_write_perm(drive->blk),
+                                           false, errp)) {
             return;
         }
     }
@@ -210,7 +210,7 @@ static void swim_drive_realize(DeviceState *qdev, Error **errp)
     dev->conf.werror = BLOCKDEV_ON_ERROR_AUTO;
 
     if (!blkconf_apply_backend_options(&dev->conf,
-                                       blk_is_read_only(dev->conf.blk),
+                                       !blk_supports_write_perm(dev->conf.blk),
                                        false, errp)) {
         return;
     }
diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index bac2d6fa2b..e8600b069d 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -1021,7 +1021,7 @@ static uint64_t virtio_blk_get_features(VirtIODevice *vdev, uint64_t features,
          virtio_has_feature(features, VIRTIO_BLK_F_CONFIG_WCE))) {
         virtio_add_feature(&features, VIRTIO_BLK_F_WCE);
     }
-    if (blk_is_read_only(s->blk)) {
+    if (!blk_is_writable(s->blk)) {
         virtio_add_feature(&features, VIRTIO_BLK_F_RO);
     }
     if (s->conf.num_queues > 1) {
@@ -1175,8 +1175,8 @@ static void virtio_blk_device_realize(DeviceState *dev, Error **errp)
     }
 
     if (!blkconf_apply_backend_options(&conf->conf,
-                                       blk_is_read_only(conf->conf.blk), true,
-                                       errp)) {
+                                       !blk_supports_write_perm(conf->conf.blk),
+                                       true, errp)) {
         return;
     }
     s->original_wce = blk_enable_write_cache(conf->conf.blk);
diff --git a/hw/block/xen-block.c b/hw/block/xen-block.c
index 718d886e5c..0e7d66c2a7 100644
--- a/hw/block/xen-block.c
+++ b/hw/block/xen-block.c
@@ -567,7 +567,7 @@ static void xen_disk_realize(XenBlockDevice *blockdev, Error **errp)
         return;
     }
 
-    blockdev->info = blk_is_read_only(conf->blk) ? VDISK_READONLY : 0;
+    blockdev->info = blk_supports_write_perm(conf->blk) ? 0 : VDISK_READONLY;
 }
 
 static void xen_disk_class_init(ObjectClass *class, void *data)