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>

block/block-backend.c

@@ -1826,17 +1826,30 @@ void blk_error_action(BlockBackend *blk, BlockErrorAction action,
     }
 }
 
-bool blk_is_read_only(BlockBackend *blk)
+/*
+ * Returns true if the BlockBackend can support taking write permissions
+ * (because its root node is not read-only).
+ */
+bool blk_supports_write_perm(BlockBackend *blk)
 {
     BlockDriverState *bs = blk_bs(blk);
 
     if (bs) {
-        return bdrv_is_read_only(bs);
+        return !bdrv_is_read_only(bs);
     } else {
-        return blk->root_state.read_only;
+        return !blk->root_state.read_only;
     }
 }
 
+/*
+ * Returns true if the BlockBackend can be written to in its current
+ * configuration (i.e. if write permission have been requested)
+ */
+bool blk_is_writable(BlockBackend *blk)
+{
+    return blk->perm & BLK_PERM_WRITE;
+}
+
 bool blk_is_sg(BlockBackend *blk)
 {
     BlockDriverState *bs = blk_bs(blk);

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;
     }

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)) {

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;

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;
         }

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;
     }
 

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;
         }

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) {

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) {

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;
     }

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);

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)

hw/ide/core.c

@@ -2537,7 +2537,7 @@ int ide_init_drive(IDEState *s, BlockBackend *blk, IDEDriveKind kind,
             error_setg(errp, "Device needs media, but drive is empty");
             return -1;
         }
-        if (blk_is_read_only(blk)) {
+        if (!blk_is_writable(blk)) {
             error_setg(errp, "Can't use a read-only drive");
             return -1;
         }

hw/misc/sifive_u_otp.c

@@ -228,7 +228,7 @@ static void sifive_u_otp_realize(DeviceState *dev, Error **errp)
 
         if (s->blk) {
             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;

hw/ppc/pnv_pnor.c

@@ -86,7 +86,7 @@ static void pnv_pnor_realize(DeviceState *dev, 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;

hw/scsi/scsi-disk.c

@@ -1270,7 +1270,7 @@ static int scsi_disk_emulate_mode_sense(SCSIDiskReq *r, uint8_t *outbuf)
 
     if (s->qdev.type == TYPE_DISK) {
         dev_specific_param = s->features & (1 << SCSI_DISK_F_DPOFUA) ? 0x10 : 0;
-        if (blk_is_read_only(s->qdev.conf.blk)) {
+        if (!blk_is_writable(s->qdev.conf.blk)) {
             dev_specific_param |= 0x80; /* Readonly.  */
         }
     } else {
@@ -1704,7 +1704,7 @@ static void scsi_disk_emulate_unmap(SCSIDiskReq *r, uint8_t *inbuf)
         goto invalid_param_len;
     }
 
-    if (blk_is_read_only(s->qdev.conf.blk)) {
+    if (!blk_is_writable(s->qdev.conf.blk)) {
         block_acct_invalid(blk_get_stats(s->qdev.conf.blk), BLOCK_ACCT_UNMAP);
         scsi_check_condition(r, SENSE_CODE(WRITE_PROTECTED));
         return;
@@ -1795,7 +1795,7 @@ static void scsi_disk_emulate_write_same(SCSIDiskReq *r, uint8_t *inbuf)
         return;
     }
 
-    if (blk_is_read_only(s->qdev.conf.blk)) {
+    if (!blk_is_writable(s->qdev.conf.blk)) {
         scsi_check_condition(r, SENSE_CODE(WRITE_PROTECTED));
         return;
     }
@@ -2207,7 +2207,7 @@ static int32_t scsi_disk_dma_command(SCSIRequest *req, uint8_t *buf)
     case WRITE_VERIFY_10:
     case WRITE_VERIFY_12:
     case WRITE_VERIFY_16:
-        if (blk_is_read_only(s->qdev.conf.blk)) {
+        if (!blk_is_writable(s->qdev.conf.blk)) {
             scsi_check_condition(r, SENSE_CODE(WRITE_PROTECTED));
             return 0;
         }
@@ -2380,7 +2380,7 @@ static void scsi_realize(SCSIDevice *dev, Error **errp)
         }
     }
 
-    read_only = blk_is_read_only(s->qdev.conf.blk);
+    read_only = !blk_supports_write_perm(s->qdev.conf.blk);
     if (dev->type == TYPE_ROM) {
         read_only = true;
     }

hw/scsi/scsi-generic.c

@@ -306,7 +306,7 @@ static void scsi_read_complete(void * opaque, int ret)
      * readonly.
      */
     if ((s->type == TYPE_DISK || s->type == TYPE_TAPE || s->type == TYPE_ZBC) &&
-        blk_is_read_only(s->conf.blk) &&
+        !blk_is_writable(s->conf.blk) &&
         (r->req.cmd.buf[0] == MODE_SENSE ||
          r->req.cmd.buf[0] == MODE_SENSE_10) &&
         (r->req.cmd.buf[1] & 0x8) == 0) {
@@ -694,7 +694,7 @@ static void scsi_generic_realize(SCSIDevice *s, Error **errp)
         return;
     }
     if (!blkconf_apply_backend_options(&s->conf,
-                                       blk_is_read_only(s->conf.blk),
+                                       !blk_supports_write_perm(s->conf.blk),
                                        true, errp)) {
         return;
     }

hw/sd/sd.c

@@ -567,7 +567,7 @@ static void sd_reset(DeviceState *dev)
     sd_set_sdstatus(sd);
 
     g_free(sd->wp_groups);
-    sd->wp_switch = sd->blk ? blk_is_read_only(sd->blk) : false;
+    sd->wp_switch = sd->blk ? !blk_is_writable(sd->blk) : false;
     sd->wpgrps_size = sect;
     sd->wp_groups = bitmap_new(sd->wpgrps_size);
     memset(sd->function_group, 0, sizeof(sd->function_group));
@@ -735,7 +735,7 @@ void sd_set_cb(SDState *sd, qemu_irq readonly, qemu_irq insert)
 {
     sd->readonly_cb = readonly;
     sd->inserted_cb = insert;
-    qemu_set_irq(readonly, sd->blk ? blk_is_read_only(sd->blk) : 0);
+    qemu_set_irq(readonly, sd->blk ? !blk_is_writable(sd->blk) : 0);
     qemu_set_irq(insert, sd->blk ? blk_is_inserted(sd->blk) : 0);
 }
 
@@ -2131,7 +2131,7 @@ static void sd_realize(DeviceState *dev, Error **errp)
     if (sd->blk) {
         int64_t blk_size;
 
-        if (blk_is_read_only(sd->blk)) {
+        if (!blk_supports_write_perm(sd->blk)) {
             error_setg(errp, "Cannot use read-only drive as SD card");
             return;
         }

hw/usb/dev-storage.c

@@ -613,8 +613,8 @@ static void usb_msd_storage_realize(USBDevice *dev, Error **errp)
         return;
     }
 
-    if (!blkconf_apply_backend_options(&s->conf, blk_is_read_only(blk), true,
-                                       errp)) {
+    if (!blkconf_apply_backend_options(&s->conf, !blk_supports_write_perm(blk),
+                                       true, errp)) {
         return;
     }
 

include/sysemu/block-backend.h

@@ -191,7 +191,8 @@ BlockErrorAction blk_get_error_action(BlockBackend *blk, bool is_read,
                                       int error);
 void blk_error_action(BlockBackend *blk, BlockErrorAction action,
                       bool is_read, int error);
-bool blk_is_read_only(BlockBackend *blk);
+bool blk_supports_write_perm(BlockBackend *blk);
+bool blk_is_writable(BlockBackend *blk);
 bool blk_is_sg(BlockBackend *blk);
 bool blk_enable_write_cache(BlockBackend *blk);
 void blk_set_enable_write_cache(BlockBackend *blk, bool wce);