30 files changed, 165 insertions, 116 deletions

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index 63ef6af..ad8b315 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -2013,7 +2013,7 @@ static int kvm_init(MachineState *ms)
 #endif
     QLIST_INIT(&s->kvm_parked_vcpus);
     s->vmfd = -1;
-    s->fd = qemu_open("/dev/kvm", O_RDWR);
+    s->fd = qemu_open_old("/dev/kvm", O_RDWR);
     if (s->fd == -1) {
         fprintf(stderr, "Could not access KVM kernel module: %m\n");
         ret = -errno;
diff --git a/backends/rng-random.c b/backends/rng-random.c
index 32998d8..245b12a 100644
--- a/backends/rng-random.c
+++ b/backends/rng-random.c
@@ -75,7 +75,7 @@ static void rng_random_opened(RngBackend *b, Error **errp)
         error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
                    "filename", "a valid filename");
     } else {
-        s->fd = qemu_open(s->filename, O_RDONLY | O_NONBLOCK);
+        s->fd = qemu_open_old(s->filename, O_RDONLY | O_NONBLOCK);
         if (s->fd == -1) {
             error_setg_file_open(errp, errno, s->filename);
         }
diff --git a/backends/tpm/tpm_passthrough.c b/backends/tpm/tpm_passthrough.c
index 10722e0..6d6294e 100644
--- a/backends/tpm/tpm_passthrough.c
+++ b/backends/tpm/tpm_passthrough.c
@@ -218,7 +218,7 @@ static int tpm_passthrough_open_sysfs_cancel(TPMPassthruState *tpm_pt)
     char path[PATH_MAX];
 
     if (tpm_pt->options->cancel_path) {
-        fd = qemu_open(tpm_pt->options->cancel_path, O_WRONLY);
+        fd = qemu_open_old(tpm_pt->options->cancel_path, O_WRONLY);
         if (fd < 0) {
             error_report("tpm_passthrough: Could not open TPM cancel path: %s",
                          strerror(errno));
@@ -236,11 +236,11 @@ static int tpm_passthrough_open_sysfs_cancel(TPMPassthruState *tpm_pt)
     dev++;
     if (snprintf(path, sizeof(path), "/sys/class/tpm/%s/device/cancel",
                  dev) < sizeof(path)) {
-        fd = qemu_open(path, O_WRONLY);
+        fd = qemu_open_old(path, O_WRONLY);
         if (fd < 0) {
             if (snprintf(path, sizeof(path), "/sys/class/misc/%s/device/cancel",
                          dev) < sizeof(path)) {
-                fd = qemu_open(path, O_WRONLY);
+                fd = qemu_open_old(path, O_WRONLY);
             }
         }
     }
@@ -272,7 +272,7 @@ tpm_passthrough_handle_device_opts(TPMPassthruState *tpm_pt, QemuOpts *opts)
     }
 
     tpm_pt->tpm_dev = value ? value : TPM_PASSTHROUGH_DEFAULT_DEVICE;
-    tpm_pt->tpm_fd = qemu_open(tpm_pt->tpm_dev, O_RDWR);
+    tpm_pt->tpm_fd = qemu_open_old(tpm_pt->tpm_dev, O_RDWR);
     if (tpm_pt->tpm_fd < 0) {
         error_report("Cannot access TPM device using '%s': %s",
                      tpm_pt->tpm_dev, strerror(errno));
diff --git a/block/file-posix.c b/block/file-posix.c
index 9a00d41..c63926d 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -630,11 +630,10 @@ static int raw_open_common(BlockDriverState *bs, QDict *options,
     raw_parse_flags(bdrv_flags, &s->open_flags, false);
 
     s->fd = -1;
-    fd = qemu_open(filename, s->open_flags, 0644);
+    fd = qemu_open(filename, s->open_flags, errp);
     ret = fd < 0 ? -errno : 0;
 
     if (ret < 0) {
-        error_setg_file_open(errp, -ret, filename);
         if (ret == -EROFS) {
             ret = -EACCES;
         }
@@ -1037,10 +1036,8 @@ static int raw_reconfigure_getfd(BlockDriverState *bs, int flags,
         const char *normalized_filename = bs->filename;
         ret = raw_normalize_devicepath(&normalized_filename, errp);
         if (ret >= 0) {
-            assert(!(*open_flags & O_CREAT));
-            fd = qemu_open(normalized_filename, *open_flags);
+            fd = qemu_open(normalized_filename, *open_flags, errp);
             if (fd == -1) {
-                error_setg_errno(errp, errno, "Could not reopen file");
                 return -1;
             }
         }
@@ -2411,10 +2408,9 @@ raw_co_create(BlockdevCreateOptions *options, Error **errp)
     }
 
     /* Create file */
-    fd = qemu_open(file_opts->filename, O_RDWR | O_CREAT | O_BINARY, 0644);
+    fd = qemu_create(file_opts->filename, O_RDWR | O_BINARY, 0644, errp);
     if (fd < 0) {
         result = -errno;
-        error_setg_errno(errp, -result, "Could not create file");
         goto out;
     }
 
@@ -3335,7 +3331,7 @@ static bool setup_cdrom(char *bsd_path, Error **errp)
     for (index = 0; index < num_of_test_partitions; index++) {
         snprintf(test_partition, sizeof(test_partition), "%ss%d", bsd_path,
                  index);
-        fd = qemu_open(test_partition, O_RDONLY | O_BINARY | O_LARGEFILE);
+        fd = qemu_open(test_partition, O_RDONLY | O_BINARY | O_LARGEFILE, NULL);
         if (fd >= 0) {
             partition_found = true;
             qemu_close(fd);
@@ -3653,7 +3649,7 @@ static int cdrom_probe_device(const char *filename)
     int prio = 0;
     struct stat st;
 
-    fd = qemu_open(filename, O_RDONLY | O_NONBLOCK);
+    fd = qemu_open(filename, O_RDONLY | O_NONBLOCK, NULL);
     if (fd < 0) {
         goto out;
     }
@@ -3787,7 +3783,7 @@ static int cdrom_reopen(BlockDriverState *bs)
      */
     if (s->fd >= 0)
         qemu_close(s->fd);
-    fd = qemu_open(bs->filename, s->open_flags, 0644);
+    fd = qemu_open(bs->filename, s->open_flags, NULL);
     if (fd < 0) {
         s->fd = -1;
         return -EIO;
diff --git a/block/file-win32.c b/block/file-win32.c
index e2900c3..2642088 100644
--- a/block/file-win32.c
+++ b/block/file-win32.c
@@ -596,10 +596,9 @@ static int raw_co_create(BlockdevCreateOptions *options, Error **errp)
         return -EINVAL;
     }
 
-    fd = qemu_open(file_opts->filename, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY,
-                   0644);
+    fd = qemu_create(file_opts->filename, O_WRONLY | O_TRUNC | O_BINARY,
+                     0644, errp);
     if (fd < 0) {
-        error_setg_errno(errp, errno, "Could not create file");
         return -EIO;
     }
     set_sparse(fd);
diff --git a/block/vvfat.c b/block/vvfat.c
index 36b53c8..5abb90e 100644
--- a/block/vvfat.c
+++ b/block/vvfat.c
@@ -1352,7 +1352,8 @@ static int open_file(BDRVVVFATState* s,mapping_t* mapping)
     if(!s->current_mapping ||
             strcmp(s->current_mapping->path,mapping->path)) {
         /* open file */
-        int fd = qemu_open(mapping->path, O_RDONLY | O_BINARY | O_LARGEFILE);
+        int fd = qemu_open_old(mapping->path,
+                               O_RDONLY | O_BINARY | O_LARGEFILE);
         if(fd<0)
             return -1;
         vvfat_close_current_file(s);
@@ -2513,7 +2514,7 @@ static int commit_one_file(BDRVVVFATState* s,
     for (i = s->cluster_size; i < offset; i += s->cluster_size)
         c = modified_fat_get(s, c);
 
-    fd = qemu_open(mapping->path, O_RDWR | O_CREAT | O_BINARY, 0666);
+    fd = qemu_open_old(mapping->path, O_RDWR | O_CREAT | O_BINARY, 0666);
     if (fd < 0) {
         fprintf(stderr, "Could not open %s... (%s, %d)\n", mapping->path,
                 strerror(errno), errno);
diff --git a/chardev/char-fd.c b/chardev/char-fd.c
index c2d8101..1cd62f2 100644
--- a/chardev/char-fd.c
+++ b/chardev/char-fd.c
@@ -119,7 +119,7 @@ int qmp_chardev_open_file_source(char *src, int flags, Error **errp)
 {
     int fd = -1;
 
-    TFR(fd = qemu_open(src, flags, 0666));
+    TFR(fd = qemu_open_old(src, flags, 0666));
     if (fd == -1) {
         error_setg_file_open(errp, errno, src);
     }
diff --git a/chardev/char-pipe.c b/chardev/char-pipe.c
index fd12c9e..7eca5d9 100644
--- a/chardev/char-pipe.c
+++ b/chardev/char-pipe.c
@@ -132,8 +132,8 @@ static void qemu_chr_open_pipe(Chardev *chr,
 
     filename_in = g_strdup_printf("%s.in", filename);
     filename_out = g_strdup_printf("%s.out", filename);
-    TFR(fd_in = qemu_open(filename_in, O_RDWR | O_BINARY));
-    TFR(fd_out = qemu_open(filename_out, O_RDWR | O_BINARY));
+    TFR(fd_in = qemu_open_old(filename_in, O_RDWR | O_BINARY));
+    TFR(fd_out = qemu_open_old(filename_out, O_RDWR | O_BINARY));
     g_free(filename_in);
     g_free(filename_out);
     if (fd_in < 0 || fd_out < 0) {
@@ -143,7 +143,7 @@ static void qemu_chr_open_pipe(Chardev *chr,
         if (fd_out >= 0) {
             close(fd_out);
         }
-        TFR(fd_in = fd_out = qemu_open(filename, O_RDWR | O_BINARY));
+        TFR(fd_in = fd_out = qemu_open_old(filename, O_RDWR | O_BINARY));
         if (fd_in < 0) {
             error_setg_file_open(errp, errno, filename);
             return;
diff --git a/chardev/char.c b/chardev/char.c
index 77e7ec8..6b85099 100644
--- a/chardev/char.c
+++ b/chardev/char.c
@@ -235,7 +235,7 @@ static void qemu_char_open(Chardev *chr, ChardevBackend *backend,
         } else {
             flags |= O_TRUNC;
         }
-        chr->logfd = qemu_open(common->logfile, flags, 0666);
+        chr->logfd = qemu_open_old(common->logfile, flags, 0666);
         if (chr->logfd < 0) {
             error_setg_errno(errp, errno,
                              "Unable to open logfile %s",
diff --git a/dump/dump.c b/dump/dump.c
index 383bc78..13fda44 100644
--- a/dump/dump.c
+++ b/dump/dump.c
@@ -1994,7 +1994,7 @@ void qmp_dump_guest_memory(bool paging, const char *file,
 #endif
 
     if  (strstart(file, "file:", &p)) {
-        fd = qemu_open(p, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY, S_IRUSR);
+        fd = qemu_open_old(p, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY, S_IRUSR);
         if (fd < 0) {
             error_setg_file_open(errp, errno, p);
             return;
diff --git a/fsdev/file-op-9p.h b/fsdev/file-op-9p.h
index f2f7772..d51cec2 100644
--- a/fsdev/file-op-9p.h
+++ b/fsdev/file-op-9p.h
@@ -64,6 +64,10 @@ typedef struct ExtendedOps {
  */
 #define V9FS_REMAP_INODES           0x00000200
 #define V9FS_FORBID_MULTIDEVS       0x00000400
+/*
+ * Disables certain performance warnings from being logged on host side.
+ */
+#define V9FS_NO_PERF_WARN           0x00000800
 
 #define V9FS_SEC_MASK               0x0000003C
 
diff --git a/hw/9pfs/9p-synth.c b/hw/9pfs/9p-synth.c
index 7eb210f..cec8c0e 100644
--- a/hw/9pfs/9p-synth.c
+++ b/hw/9pfs/9p-synth.c
@@ -541,6 +541,8 @@ static int synth_init(FsContext *ctx, Error **errp)
     QLIST_INIT(&synth_root.child);
     qemu_mutex_init(&synth_mutex);
 
+    ctx->export_flags |= V9FS_NO_PERF_WARN;
+
     /* Add "." and ".." entries for root */
     v9fs_add_dir_node(&synth_root, synth_root.attr->mode,
                       "..", synth_root.attr, synth_root.attr->inode);
diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
index 7bb994b..741d222 100644
--- a/hw/9pfs/9p.c
+++ b/hw/9pfs/9p.c
@@ -1353,6 +1353,15 @@ static void coroutine_fn v9fs_version(void *opaque)
         goto out;
     }
 
+    /* 8192 is the default msize of Linux clients */
+    if (s->msize <= 8192 && !(s->ctx.export_flags & V9FS_NO_PERF_WARN)) {
+        warn_report_once(
+            "9p: degraded performance: a reasonable high msize should be "
+            "chosen on client/guest side (chosen msize is <= 8192). See "
+            "https://wiki.qemu.org/Documentation/9psetup#msize for details."
+        );
+    }
+
 marshal:
     err = pdu_marshal(pdu, offset, "ds", s->msize, &version);
     if (err < 0) {
diff --git a/hw/s390x/s390-skeys.c b/hw/s390x/s390-skeys.c
index db2f49c..5cc559f 100644
--- a/hw/s390x/s390-skeys.c
+++ b/hw/s390x/s390-skeys.c
@@ -125,7 +125,7 @@ void qmp_dump_skeys(const char *filename, Error **errp)
         return;
     }
 
-    fd = qemu_open(filename, O_WRONLY | O_CREAT | O_TRUNC, 0600);
+    fd = qemu_open_old(filename, O_WRONLY | O_CREAT | O_TRUNC, 0600);
     if (fd < 0) {
         error_setg_file_open(errp, errno, filename);
         return;
diff --git a/hw/usb/host-libusb.c b/hw/usb/host-libusb.c
index 43c9350..8b02bee 100644
--- a/hw/usb/host-libusb.c
+++ b/hw/usb/host-libusb.c
@@ -1147,7 +1147,7 @@ static void usb_host_realize(USBDevice *udev, Error **errp)
     if (s->hostdevice) {
         int fd;
         s->needs_autoscan = false;
-        fd = qemu_open(s->hostdevice, O_RDWR);
+        fd = qemu_open_old(s->hostdevice, O_RDWR);
         if (fd < 0) {
             error_setg_errno(errp, errno, "failed to open %s", s->hostdevice);
             return;
diff --git a/hw/usb/u2f-passthru.c b/hw/usb/u2f-passthru.c
index e9c8aa4..ae00e93 100644
--- a/hw/usb/u2f-passthru.c
+++ b/hw/usb/u2f-passthru.c
@@ -383,7 +383,7 @@ static int u2f_passthru_open_from_device(struct udev_device *device)
 {
     const char *devnode = udev_device_get_devnode(device);
 
-    int fd = qemu_open(devnode, O_RDWR);
+    int fd = qemu_open_old(devnode, O_RDWR);
     if (fd < 0) {
         return -1;
     } else if (!u2f_passthru_is_u2f_device(fd)) {
@@ -482,7 +482,7 @@ static void u2f_passthru_realize(U2FKeyState *base, Error **errp)
         return;
 #endif
     } else {
-        fd = qemu_open(key->hidraw, O_RDWR);
+        fd = qemu_open_old(key->hidraw, O_RDWR);
         if (fd < 0) {
             error_setg(errp, "%s: Failed to open %s", TYPE_U2F_PASSTHRU,
                        key->hidraw);
diff --git a/hw/vfio/common.c b/hw/vfio/common.c
index 3335714..13471ae 100644
--- a/hw/vfio/common.c
+++ b/hw/vfio/common.c
@@ -1254,7 +1254,7 @@ static int vfio_connect_container(VFIOGroup *group, AddressSpace *as,
         }
     }
 
-    fd = qemu_open("/dev/vfio/vfio", O_RDWR);
+    fd = qemu_open_old("/dev/vfio/vfio", O_RDWR);
     if (fd < 0) {
         error_setg_errno(errp, errno, "failed to open /dev/vfio/vfio");
         ret = -errno;
@@ -1479,7 +1479,7 @@ VFIOGroup *vfio_get_group(int groupid, AddressSpace *as, Error **errp)
     group = g_malloc0(sizeof(*group));
 
     snprintf(path, sizeof(path), "/dev/vfio/%d", groupid);
-    group->fd = qemu_open(path, O_RDWR);
+    group->fd = qemu_open_old(path, O_RDWR);
     if (group->fd < 0) {
         error_setg_errno(errp, errno, "failed to open %s", path);
         goto free_group_exit;
diff --git a/include/monitor/monitor.h b/include/monitor/monitor.h
index 1018d75..c017077 100644
--- a/include/monitor/monitor.h
+++ b/include/monitor/monitor.h
@@ -43,8 +43,7 @@ int monitor_read_password(MonitorHMP *mon, ReadLineFunc *readline_func,
 AddfdInfo *monitor_fdset_add_fd(int fd, bool has_fdset_id, int64_t fdset_id,
                                 bool has_opaque, const char *opaque,
                                 Error **errp);
-int monitor_fdset_get_fd(int64_t fdset_id, int flags);
-int monitor_fdset_dup_fd_add(int64_t fdset_id, int dup_fd);
+int monitor_fdset_dup_fd_add(int64_t fdset_id, int flags);
 void monitor_fdset_dup_fd_remove(int dup_fd);
 int64_t monitor_fdset_dup_fd_find(int dup_fd);
 
diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
index e80fddd..dad44be 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -497,10 +497,17 @@ int qemu_madvise(void *addr, size_t len, int advice);
 int qemu_mprotect_rwx(void *addr, size_t size);
 int qemu_mprotect_none(void *addr, size_t size);
 
-int qemu_open(const char *name, int flags, ...);
+/*
+ * Don't introduce new usage of this function, prefer the following
+ * qemu_open/qemu_create that take an "Error **errp"
+ */
+int qemu_open_old(const char *name, int flags, ...);
+int qemu_open(const char *name, int flags, Error **errp);
+int qemu_create(const char *name, int flags, mode_t mode, Error **errp);
 int qemu_close(int fd);
 int qemu_unlink(const char *name);
 #ifndef _WIN32
+int qemu_dup_flags(int fd, int flags);
 int qemu_dup(int fd);
 int qemu_lock_fd(int fd, int64_t start, int64_t len, bool exclusive);
 int qemu_unlock_fd(int fd, int64_t start, int64_t len);
diff --git a/io/channel-file.c b/io/channel-file.c
index dac21f6..2ed3b75 100644
--- a/io/channel-file.c
+++ b/io/channel-file.c
@@ -51,7 +51,7 @@ qio_channel_file_new_path(const char *path,
 
     ioc = QIO_CHANNEL_FILE(object_new(TYPE_QIO_CHANNEL_FILE));
 
-    ioc->fd = qemu_open(path, flags, mode);
+    ioc->fd = qemu_open_old(path, flags, mode);
     if (ioc->fd < 0) {
         object_unref(OBJECT(ioc));
         error_setg_errno(errp, errno,
diff --git a/monitor/misc.c b/monitor/misc.c
index e847b58..0b1b9b1 100644
--- a/monitor/misc.c
+++ b/monitor/misc.c
@@ -1547,69 +1547,61 @@ AddfdInfo *monitor_fdset_add_fd(int fd, bool has_fdset_id, int64_t fdset_id,
     return fdinfo;
 }
 
-int monitor_fdset_get_fd(int64_t fdset_id, int flags)
+int monitor_fdset_dup_fd_add(int64_t fdset_id, int flags)
 {
 #ifdef _WIN32
     return -ENOENT;
 #else
     MonFdset *mon_fdset;
-    MonFdsetFd *mon_fdset_fd;
-    int mon_fd_flags;
-    int ret;
 
     qemu_mutex_lock(&mon_fdsets_lock);
     QLIST_FOREACH(mon_fdset, &mon_fdsets, next) {
+        MonFdsetFd *mon_fdset_fd;
+        MonFdsetFd *mon_fdset_fd_dup;
+        int fd = -1;
+        int dup_fd;
+        int mon_fd_flags;
+
         if (mon_fdset->id != fdset_id) {
             continue;
         }
+
         QLIST_FOREACH(mon_fdset_fd, &mon_fdset->fds, next) {
             mon_fd_flags = fcntl(mon_fdset_fd->fd, F_GETFL);
             if (mon_fd_flags == -1) {
-                ret = -errno;
-                goto out;
+                qemu_mutex_unlock(&mon_fdsets_lock);
+                return -1;
             }
 
             if ((flags & O_ACCMODE) == (mon_fd_flags & O_ACCMODE)) {
-                ret = mon_fdset_fd->fd;
-                goto out;
+                fd = mon_fdset_fd->fd;
+                break;
             }
         }
-        ret = -EACCES;
-        goto out;
-    }
-    ret = -ENOENT;
-
-out:
-    qemu_mutex_unlock(&mon_fdsets_lock);
-    return ret;
-#endif
-}
-
-int monitor_fdset_dup_fd_add(int64_t fdset_id, int dup_fd)
-{
-    MonFdset *mon_fdset;
-    MonFdsetFd *mon_fdset_fd_dup;
 
-    qemu_mutex_lock(&mon_fdsets_lock);
-    QLIST_FOREACH(mon_fdset, &mon_fdsets, next) {
-        if (mon_fdset->id != fdset_id) {
-            continue;
+        if (fd == -1) {
+            qemu_mutex_unlock(&mon_fdsets_lock);
+            errno = EACCES;
+            return -1;
         }
-        QLIST_FOREACH(mon_fdset_fd_dup, &mon_fdset->dup_fds, next) {
-            if (mon_fdset_fd_dup->fd == dup_fd) {
-                goto err;
-            }
+
+        dup_fd = qemu_dup_flags(fd, flags);
+        if (dup_fd == -1) {
+            qemu_mutex_unlock(&mon_fdsets_lock);
+            return -1;
         }
+
         mon_fdset_fd_dup = g_malloc0(sizeof(*mon_fdset_fd_dup));
         mon_fdset_fd_dup->fd = dup_fd;
         QLIST_INSERT_HEAD(&mon_fdset->dup_fds, mon_fdset_fd_dup, next);
         qemu_mutex_unlock(&mon_fdsets_lock);
-        return 0;
+        return dup_fd;
     }
 
-err:
     qemu_mutex_unlock(&mon_fdsets_lock);
+    errno = ENOENT;
     return -1;
+#endif
 }
 
 static int64_t monitor_fdset_dup_fd_find_remove(int dup_fd, bool remove)
diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
index bc0e0d2..e2b3ba8 100644
--- a/net/vhost-vdpa.c
+++ b/net/vhost-vdpa.c
@@ -184,7 +184,7 @@ static int net_vhost_vdpa_init(NetClientState *peer, const char *device,
     snprintf(nc->info_str, sizeof(nc->info_str), TYPE_VHOST_VDPA);
     nc->queue_index = 0;
     s = DO_UPCAST(VhostVDPAState, nc, nc);
-    vdpa_device_fd = qemu_open(vhostdev, O_RDWR);
+    vdpa_device_fd = qemu_open_old(vhostdev, O_RDWR);
     if (vdpa_device_fd == -1) {
         return -errno;
     }
diff --git a/os-posix.c b/os-posix.c
index bf98508..0bfd8e2 100644
--- a/os-posix.c
+++ b/os-posix.c
@@ -297,7 +297,7 @@ void os_setup_post(void)
             error_report("not able to chdir to /: %s", strerror(errno));
             exit(1);
         }
-        TFR(fd = qemu_open("/dev/null", O_RDWR));
+        TFR(fd = qemu_open_old("/dev/null", O_RDWR));
         if (fd == -1) {
             exit(1);
         }
diff --git a/qga/channel-posix.c b/qga/channel-posix.c
index 8fc205a..0373975 100644
--- a/qga/channel-posix.c
+++ b/qga/channel-posix.c
@@ -127,7 +127,7 @@ static gboolean ga_channel_open(GAChannel *c, const gchar *path,
     switch (c->method) {
     case GA_CHANNEL_VIRTIO_SERIAL: {
         assert(fd < 0);
-        fd = qemu_open(path, O_RDWR | O_NONBLOCK
+        fd = qemu_open_old(path, O_RDWR | O_NONBLOCK
 #ifndef CONFIG_SOLARIS
                            | O_ASYNC
 #endif
@@ -157,7 +157,7 @@ static gboolean ga_channel_open(GAChannel *c, const gchar *path,
         struct termios tio;
 
         assert(fd < 0);
-        fd = qemu_open(path, O_RDWR | O_NOCTTY | O_NONBLOCK);
+        fd = qemu_open_old(path, O_RDWR | O_NOCTTY | O_NONBLOCK);
         if (fd == -1) {
             g_critical("error opening channel: %s", strerror(errno));
             return false;
diff --git a/qga/commands-posix.c b/qga/commands-posix.c
index af5a58a..3bffee9 100644
--- a/qga/commands-posix.c
+++ b/qga/commands-posix.c
@@ -1365,7 +1365,7 @@ int64_t qmp_guest_fsfreeze_freeze_list(bool has_mountpoints,
             }
         }
 
-        fd = qemu_open(mount->dirname, O_RDONLY);
+        fd = qemu_open_old(mount->dirname, O_RDONLY);
         if (fd == -1) {
             error_setg_errno(errp, errno, "failed to open %s", mount->dirname);
             goto error;
@@ -1432,7 +1432,7 @@ int64_t qmp_guest_fsfreeze_thaw(Error **errp)
 
     QTAILQ_FOREACH(mount, &mounts, next) {
         logged = false;
-        fd = qemu_open(mount->dirname, O_RDONLY);
+        fd = qemu_open_old(mount->dirname, O_RDONLY);
         if (fd == -1) {
             continue;
         }
@@ -1522,7 +1522,7 @@ qmp_guest_fstrim(bool has_minimum, int64_t minimum, Error **errp)
         list->next = response->paths;
         response->paths = list;
 
-        fd = qemu_open(mount->dirname, O_RDONLY);
+        fd = qemu_open_old(mount->dirname, O_RDONLY);
         if (fd == -1) {
             result->error = g_strdup_printf("failed to open: %s",
                                             strerror(errno));
diff --git a/stubs/fdset.c b/stubs/fdset.c
index 67dd5e1..56b3663 100644
--- a/stubs/fdset.c
+++ b/stubs/fdset.c
@@ -1,8 +1,9 @@
 #include "qemu/osdep.h"
 #include "monitor/monitor.h"
 
-int monitor_fdset_dup_fd_add(int64_t fdset_id, int dup_fd)
+int monitor_fdset_dup_fd_add(int64_t fdset_id, int flags)
 {
+    errno = ENOSYS;
     return -1;
 }
 
@@ -11,11 +12,6 @@ int64_t monitor_fdset_dup_fd_find(int dup_fd)
     return -1;
 }
 
-int monitor_fdset_get_fd(int64_t fdset_id, int flags)
-{
-    return -ENOENT;
-}
-
 void monitor_fdset_dup_fd_remove(int dupfd)
 {
 }
diff --git a/target/arm/kvm.c b/target/arm/kvm.c
index 2eae733..0dcb9bf 100644
--- a/target/arm/kvm.c
+++ b/target/arm/kvm.c
@@ -71,7 +71,7 @@ bool kvm_arm_create_scratch_host_vcpu(const uint32_t *cpus_to_try,
 {
     int ret = 0, kvmfd = -1, vmfd = -1, cpufd = -1;
 
-    kvmfd = qemu_open("/dev/kvm", O_RDWR);
+    kvmfd = qemu_open_old("/dev/kvm", O_RDWR);
     if (kvmfd < 0) {
         goto err;
     }
diff --git a/ui/console.c b/ui/console.c
index f8d7643..7592c3c 100644
--- a/ui/console.c
+++ b/ui/console.c
@@ -373,7 +373,7 @@ void qmp_screendump(const char *filename, bool has_device, const char *device,
         return;
     }
 
-    fd = qemu_open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY, 0666);
+    fd = qemu_open_old(filename, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY, 0666);
     if (fd == -1) {
         error_setg(errp, "failed to open file '%s': %s", filename,
                    strerror(errno));
diff --git a/util/osdep.c b/util/osdep.c
index 4829c07..8ea7a80 100644
--- a/util/osdep.c
+++ b/util/osdep.c
@@ -22,6 +22,7 @@
  * THE SOFTWARE.
  */
 #include "qemu/osdep.h"
+#include "qapi/error.h"
 
 /* Needed early for CONFIG_BSD etc. */
 
@@ -122,7 +123,7 @@ static int fcntl_op_getlk = -1;
 /*
  * Dups an fd and sets the flags
  */
-static int qemu_dup_flags(int fd, int flags)
+int qemu_dup_flags(int fd, int flags)
 {
     int ret;
     int serrno;
@@ -279,13 +280,27 @@ int qemu_lock_fd_test(int fd, int64_t start, int64_t len, bool exclusive)
 }
 #endif
 
+static int qemu_open_cloexec(const char *name, int flags, mode_t mode)
+{
+    int ret;
+#ifdef O_CLOEXEC
+    ret = open(name, flags | O_CLOEXEC, mode);
+#else
+    ret = open(name, flags, mode);
+    if (ret >= 0) {
+        qemu_set_cloexec(ret);
+    }
+#endif
+    return ret;
+}
+
 /*
  * Opens a file with FD_CLOEXEC set
  */
-int qemu_open(const char *name, int flags, ...)
+static int
+qemu_open_internal(const char *name, int flags, mode_t mode, Error **errp)
 {
     int ret;
-    int mode = 0;
 
 #ifndef _WIN32
     const char *fdset_id_str;
@@ -293,29 +308,19 @@ int qemu_open(const char *name, int flags, ...)
     /* Attempt dup of fd from fd set */
     if (strstart(name, "/dev/fdset/", &fdset_id_str)) {
         int64_t fdset_id;
-        int fd, dupfd;
+        int dupfd;
 
         fdset_id = qemu_parse_fdset(fdset_id_str);
         if (fdset_id == -1) {
+            error_setg(errp, "Could not parse fdset %s", name);
             errno = EINVAL;
             return -1;
         }
 
-        fd = monitor_fdset_get_fd(fdset_id, flags);
-        if (fd < 0) {
-            errno = -fd;
-            return -1;
-        }
-
-        dupfd = qemu_dup_flags(fd, flags);
+        dupfd = monitor_fdset_dup_fd_add(fdset_id, flags);
         if (dupfd == -1) {
-            return -1;
-        }
-
-        ret = monitor_fdset_dup_fd_add(fdset_id, dupfd);
-        if (ret == -1) {
-            close(dupfd);
-            errno = EINVAL;
+            error_setg_errno(errp, errno, "Could not dup FD for %s flags %x",
+                             name, flags);
             return -1;
         }
 
@@ -323,22 +328,61 @@ int qemu_open(const char *name, int flags, ...)
     }
 #endif
 
-    if (flags & O_CREAT) {
-        va_list ap;
+    ret = qemu_open_cloexec(name, flags, mode);
 
-        va_start(ap, flags);
-        mode = va_arg(ap, int);
-        va_end(ap);
+    if (ret == -1) {
+        const char *action = flags & O_CREAT ? "create" : "open";
+#ifdef O_DIRECT
+        /* Give more helpful error message for O_DIRECT */
+        if (errno == EINVAL && (flags & O_DIRECT)) {
+            ret = open(name, flags & ~O_DIRECT, mode);
+            if (ret != -1) {
+                close(ret);
+                error_setg(errp, "Could not %s '%s': "
+                           "filesystem does not support O_DIRECT",
+                           action, name);
+                errno = EINVAL; /* restore first open()'s errno */
+                return -1;
+            }
+        }
+#endif /* O_DIRECT */
+        error_setg_errno(errp, errno, "Could not %s '%s'",
+                         action, name);
     }
 
-#ifdef O_CLOEXEC
-    ret = open(name, flags | O_CLOEXEC, mode);
-#else
-    ret = open(name, flags, mode);
-    if (ret >= 0) {
-        qemu_set_cloexec(ret);
+    return ret;
+}
+
+
+int qemu_open(const char *name, int flags, Error **errp)
+{
+    assert(!(flags & O_CREAT));
+
+    return qemu_open_internal(name, flags, 0, errp);
+}
+
+
+int qemu_create(const char *name, int flags, mode_t mode, Error **errp)
+{
+    assert(!(flags & O_CREAT));
+
+    return qemu_open_internal(name, flags | O_CREAT, mode, errp);
+}
+
+
+int qemu_open_old(const char *name, int flags, ...)
+{
+    va_list ap;
+    mode_t mode = 0;
+    int ret;
+
+    va_start(ap, flags);
+    if (flags & O_CREAT) {
+        mode = va_arg(ap, int);
     }
-#endif
+    va_end(ap);
+
+    ret = qemu_open_internal(name, flags, mode, NULL);
 
 #ifdef O_DIRECT
     if (ret == -1 && errno == EINVAL && (flags & O_DIRECT)) {
diff --git a/util/oslib-posix.c b/util/oslib-posix.c
index ad8001a..f5f676f 100644
--- a/util/oslib-posix.c
+++ b/util/oslib-posix.c
@@ -125,7 +125,7 @@ bool qemu_write_pidfile(const char *path, Error **errp)
             .l_len = 0,
         };
 
-        fd = qemu_open(path, O_CREAT | O_WRONLY, S_IRUSR | S_IWUSR);
+        fd = qemu_open_old(path, O_CREAT | O_WRONLY, S_IRUSR | S_IWUSR);
         if (fd == -1) {
             error_setg_errno(errp, errno, "Cannot open pid file");
             return false;