usb: mtp filesharing

Implementation of a USB Media Transfer Device device for easy
filesharing.  Read-only.  No access control inside qemu, it will
happily export any file it is able to open to the guest, i.e.
standard unix access rights for the qemu process apply.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

2 files changed, 1107 insertions, 0 deletions

diff --git a/hw/usb/Makefile.objs b/hw/usb/Makefile.objs
index 97b457541f..17d460cb04 100644
--- a/hw/usb/Makefile.objs
+++ b/hw/usb/Makefile.objs
@@ -26,6 +26,10 @@ common-obj-y                          += ccid-card-passthru.o
 common-obj-$(CONFIG_SMARTCARD_NSS)    += ccid-card-emulated.o
 endif
 
+ifeq ($(CONFIG_POSIX),y)
+common-obj-$(CONFIG_USB_STORAGE_MTP)  += dev-mtp.o
+endif
+
 # usb redirection
 common-obj-$(CONFIG_USB_REDIR) += redirect.o quirks.o
 
diff --git a/hw/usb/dev-mtp.c b/hw/usb/dev-mtp.c
new file mode 100644
index 0000000000..8b44032900
--- /dev/null
+++ b/hw/usb/dev-mtp.c
@@ -0,0 +1,1103 @@
+/*
+ * Media Transfer Protocol implementation, backed by host filesystem.
+ *
+ * Copyright Red Hat, Inc 2014
+ *
+ * Author:
+ *   Gerd Hoffmann <kraxel@redhat.com>
+ *
+ * This code is licensed under the GPL v2 or later.
+ */
+
+#include <wchar.h>
+#include <dirent.h>
+#include <unistd.h>
+
+#include <sys/stat.h>
+#include <sys/statvfs.h>
+
+#include "qemu-common.h"
+#include "qemu/iov.h"
+#include "trace.h"
+#include "hw/usb.h"
+#include "hw/usb/desc.h"
+
+/* ----------------------------------------------------------------------- */
+
+enum mtp_container_type {
+    TYPE_COMMAND  = 1,
+    TYPE_DATA     = 2,
+    TYPE_RESPONSE = 3,
+    TYPE_EVENT    = 4,
+};
+
+enum mtp_code {
+    /* command codes */
+    CMD_GET_DEVICE_INFO            = 0x1001,
+    CMD_OPEN_SESSION               = 0x1002,
+    CMD_CLOSE_SESSION              = 0x1003,
+    CMD_GET_STORAGE_IDS            = 0x1004,
+    CMD_GET_STORAGE_INFO           = 0x1005,
+    CMD_GET_NUM_OBJECTS            = 0x1006,
+    CMD_GET_OBJECT_HANDLES         = 0x1007,
+    CMD_GET_OBJECT_INFO            = 0x1008,
+    CMD_GET_OBJECT                 = 0x1009,
+    CMD_GET_PARTIAL_OBJECT         = 0x101b,
+
+    /* response codes */
+    RES_OK                         = 0x2001,
+    RES_SESSION_NOT_OPEN           = 0x2003,
+    RES_INVALID_TRANSACTION_ID     = 0x2004,
+    RES_OPERATION_NOT_SUPPORTED    = 0x2005,
+    RES_PARAMETER_NOT_SUPPORTED    = 0x2006,
+    RES_INVALID_STORAGE_ID         = 0x2008,
+    RES_INVALID_OBJECT_HANDLE      = 0x2009,
+    RES_SPEC_BY_FORMAT_UNSUPPORTED = 0x2014,
+    RES_INVALID_PARENT_OBJECT      = 0x201a,
+    RES_INVALID_PARAMETER          = 0x201d,
+    RES_SESSION_ALREADY_OPEN       = 0x201e,
+
+    /* format codes */
+    FMT_UNDEFINED_OBJECT           = 0x3000,
+    FMT_ASSOCIATION                = 0x3001,
+};
+
+typedef struct {
+    uint32_t length;
+    uint16_t type;
+    uint16_t code;
+    uint32_t trans;
+} QEMU_PACKED mtp_container;
+
+/* ----------------------------------------------------------------------- */
+
+typedef struct MTPState MTPState;
+typedef struct MTPControl MTPControl;
+typedef struct MTPData MTPData;
+typedef struct MTPObject MTPObject;
+
+enum {
+    EP_DATA_IN = 1,
+    EP_DATA_OUT,
+    EP_EVENT,
+};
+
+struct MTPControl {
+    uint16_t     code;
+    uint32_t     trans;
+    int          argc;
+    uint32_t     argv[5];
+};
+
+struct MTPData {
+    uint16_t     code;
+    uint32_t     trans;
+    uint32_t     offset;
+    uint32_t     length;
+    uint32_t     alloc;
+    uint8_t      *data;
+    bool         first;
+    int          fd;
+};
+
+struct MTPObject {
+    uint32_t     handle;
+    uint16_t     format;
+    char         *name;
+    char         *path;
+    struct stat  stat;
+    MTPObject    *parent;
+    MTPObject    **children;
+    int32_t      nchildren;
+    QTAILQ_ENTRY(MTPObject) next;
+};
+
+struct MTPState {
+    USBDevice    dev;
+    char         *root;
+    char         *desc;
+    uint32_t     flags;
+
+    MTPData      *data_in;
+    MTPData      *data_out;
+    MTPControl   *result;
+    uint32_t     session;
+    uint32_t     next_handle;
+
+    QTAILQ_HEAD(, MTPObject) objects;
+};
+
+#define QEMU_STORAGE_ID 0x00010001
+
+#define MTP_FLAG_WRITABLE 0
+
+#define FLAG_SET(_mtp, _flag)  ((_mtp)->flags & (1 << (_flag)))
+
+/* ----------------------------------------------------------------------- */
+
+#define MTP_MANUFACTURER  "QEMU"
+#define MTP_PRODUCT       "QEMU filesharing"
+
+enum {
+    STR_MANUFACTURER = 1,
+    STR_PRODUCT,
+    STR_SERIALNUMBER,
+    STR_CONFIG_FULL,
+    STR_CONFIG_HIGH,
+    STR_CONFIG_SUPER,
+};
+
+static const USBDescStrings desc_strings = {
+    [STR_MANUFACTURER] = MTP_MANUFACTURER,
+    [STR_PRODUCT]      = MTP_PRODUCT,
+    [STR_SERIALNUMBER] = "34617",
+    [STR_CONFIG_FULL]  = "Full speed config (usb 1.1)",
+    [STR_CONFIG_HIGH]  = "High speed config (usb 2.0)",
+    [STR_CONFIG_SUPER] = "Super speed config (usb 3.0)",
+};
+
+static const USBDescIface desc_iface_full = {
+    .bInterfaceNumber              = 0,
+    .bNumEndpoints                 = 3,
+    .bInterfaceClass               = USB_CLASS_STILL_IMAGE,
+    .bInterfaceSubClass            = 0x01,
+    .bInterfaceProtocol            = 0x01,
+    .eps = (USBDescEndpoint[]) {
+        {
+            .bEndpointAddress      = USB_DIR_IN | EP_DATA_IN,
+            .bmAttributes          = USB_ENDPOINT_XFER_BULK,
+            .wMaxPacketSize        = 64,
+        },{
+            .bEndpointAddress      = USB_DIR_OUT | EP_DATA_OUT,
+            .bmAttributes          = USB_ENDPOINT_XFER_BULK,
+            .wMaxPacketSize        = 64,
+        },{
+            .bEndpointAddress      = USB_DIR_IN | EP_EVENT,
+            .bmAttributes          = USB_ENDPOINT_XFER_INT,
+            .wMaxPacketSize        = 8,
+            .bInterval             = 0x0a,
+        },
+    }
+};
+
+static const USBDescDevice desc_device_full = {
+    .bcdUSB                        = 0x0200,
+    .bMaxPacketSize0               = 8,
+    .bNumConfigurations            = 1,
+    .confs = (USBDescConfig[]) {
+        {
+            .bNumInterfaces        = 1,
+            .bConfigurationValue   = 1,
+            .iConfiguration        = STR_CONFIG_FULL,
+            .bmAttributes          = USB_CFG_ATT_ONE | USB_CFG_ATT_WAKEUP,
+            .bMaxPower             = 2,
+            .nif = 1,
+            .ifs = &desc_iface_full,
+        },
+    },
+};
+
+static const USBDescIface desc_iface_high = {
+    .bInterfaceNumber              = 0,
+    .bNumEndpoints                 = 3,
+    .bInterfaceClass               = USB_CLASS_STILL_IMAGE,
+    .bInterfaceSubClass            = 0x01,
+    .bInterfaceProtocol            = 0x01,
+    .eps = (USBDescEndpoint[]) {
+        {
+            .bEndpointAddress      = USB_DIR_IN | EP_DATA_IN,
+            .bmAttributes          = USB_ENDPOINT_XFER_BULK,
+            .wMaxPacketSize        = 512,
+        },{
+            .bEndpointAddress      = USB_DIR_OUT | EP_DATA_OUT,
+            .bmAttributes          = USB_ENDPOINT_XFER_BULK,
+            .wMaxPacketSize        = 512,
+        },{
+            .bEndpointAddress      = USB_DIR_IN | EP_EVENT,
+            .bmAttributes          = USB_ENDPOINT_XFER_INT,
+            .wMaxPacketSize        = 8,
+            .bInterval             = 0x0a,
+        },
+    }
+};
+
+static const USBDescDevice desc_device_high = {
+    .bcdUSB                        = 0x0200,
+    .bMaxPacketSize0               = 64,
+    .bNumConfigurations            = 1,
+    .confs = (USBDescConfig[]) {
+        {
+            .bNumInterfaces        = 1,
+            .bConfigurationValue   = 1,
+            .iConfiguration        = STR_CONFIG_HIGH,
+            .bmAttributes          = USB_CFG_ATT_ONE | USB_CFG_ATT_WAKEUP,
+            .bMaxPower             = 2,
+            .nif = 1,
+            .ifs = &desc_iface_high,
+        },
+    },
+};
+
+static const USBDescMSOS desc_msos = {
+    .CompatibleID = "MTP",
+    .SelectiveSuspendEnabled = true,
+};
+
+static const USBDesc desc = {
+    .id = {
+        .idVendor          = 0x46f4, /* CRC16() of "QEMU" */
+        .idProduct         = 0x0004,
+        .bcdDevice         = 0,
+        .iManufacturer     = STR_MANUFACTURER,
+        .iProduct          = STR_PRODUCT,
+        .iSerialNumber     = STR_SERIALNUMBER,
+    },
+    .full  = &desc_device_full,
+    .high  = &desc_device_high,
+    .str   = desc_strings,
+    .msos  = &desc_msos,
+};
+
+/* ----------------------------------------------------------------------- */
+
+static MTPObject *usb_mtp_object_alloc(MTPState *s, uint32_t handle,
+                                       MTPObject *parent, char *name)
+{
+    MTPObject *o = g_new0(MTPObject, 1);
+
+    if (name[0] == '.') {
+        goto ignore;
+    }
+
+    o->handle = handle;
+    o->parent = parent;
+    o->name = g_strdup(name);
+    o->nchildren = -1;
+    if (parent == NULL) {
+        o->path = g_strdup(name);
+    } else {
+        o->path = g_strdup_printf("%s/%s", parent->path, name);
+    }
+
+    if (lstat(o->path, &o->stat) != 0) {
+        goto ignore;
+    }
+    if (S_ISREG(o->stat.st_mode)) {
+        o->format = FMT_UNDEFINED_OBJECT;
+    } else if (S_ISDIR(o->stat.st_mode)) {
+        o->format = FMT_ASSOCIATION;
+    } else {
+        goto ignore;
+    }
+
+    if (access(o->path, R_OK) != 0) {
+        goto ignore;
+    }
+
+    fprintf(stderr, "%s: 0x%x %s\n", __func__, o->handle, o->path);
+
+    QTAILQ_INSERT_TAIL(&s->objects, o, next);
+    return o;
+
+ignore:
+    g_free(o->name);
+    g_free(o->path);
+    g_free(o);
+    return NULL;
+}
+
+static void usb_mtp_object_free(MTPState *s, MTPObject *o)
+{
+    int i;
+
+    fprintf(stderr, "%s: 0x%x %s\n", __func__, o->handle, o->path);
+
+    QTAILQ_REMOVE(&s->objects, o, next);
+    for (i = 0; i < o->nchildren; i++) {
+        usb_mtp_object_free(s, o->children[i]);
+    }
+    g_free(o->children);
+    g_free(o->name);
+    g_free(o->path);
+    g_free(o);
+}
+
+static MTPObject *usb_mtp_object_lookup(MTPState *s, uint32_t handle)
+{
+    MTPObject *o;
+
+    QTAILQ_FOREACH(o, &s->objects, next) {
+        if (o->handle == handle) {
+            return o;
+        }
+    }
+    return NULL;
+}
+
+static void usb_mtp_object_readdir(MTPState *s, MTPObject *o)
+{
+    struct dirent *entry;
+    DIR *dir;
+
+    o->nchildren = 0;
+    dir = opendir(o->path);
+    if (!dir) {
+        return;
+    }
+    while ((entry = readdir(dir)) != NULL) {
+        if ((o->nchildren % 32) == 0) {
+            o->children = g_realloc(o->children,
+                                    (o->nchildren + 32) * sizeof(MTPObject *));
+        }
+        o->children[o->nchildren] =
+            usb_mtp_object_alloc(s, s->next_handle++, o, entry->d_name);
+        if (o->children[o->nchildren] != NULL) {
+            o->nchildren++;
+        }
+    }
+    closedir(dir);
+}
+
+/* ----------------------------------------------------------------------- */
+
+static MTPData *usb_mtp_data_alloc(MTPControl *c)
+{
+    MTPData *data = g_new0(MTPData, 1);
+
+    data->code  = c->code;
+    data->trans = c->trans;
+    data->fd    = -1;
+    data->first = true;
+    return data;
+}
+
+static void usb_mtp_data_free(MTPData *data)
+{
+    if (data == NULL) {
+        return;
+    }
+    if (data->fd != -1) {
+        close(data->fd);
+    }
+    g_free(data->data);
+    g_free(data);
+}
+
+static void usb_mtp_realloc(MTPData *data, uint32_t bytes)
+{
+    if (data->length + bytes <= data->alloc) {
+        return;
+    }
+    data->alloc = (data->length + bytes + 0xff) & ~0xff;
+    data->data  = g_realloc(data->data, data->alloc);
+}
+
+static void usb_mtp_add_u8(MTPData *data, uint8_t val)
+{
+    usb_mtp_realloc(data, 1);
+    data->data[data->length++] = val;
+}
+
+static void usb_mtp_add_u16(MTPData *data, uint16_t val)
+{
+    usb_mtp_realloc(data, 2);
+    data->data[data->length++] = (val >> 0) & 0xff;
+    data->data[data->length++] = (val >> 8) & 0xff;
+}
+
+static void usb_mtp_add_u32(MTPData *data, uint32_t val)
+{
+    usb_mtp_realloc(data, 4);
+    data->data[data->length++] = (val >>  0) & 0xff;
+    data->data[data->length++] = (val >>  8) & 0xff;
+    data->data[data->length++] = (val >> 16) & 0xff;
+    data->data[data->length++] = (val >> 24) & 0xff;
+}
+
+static void usb_mtp_add_u64(MTPData *data, uint64_t val)
+{
+    usb_mtp_realloc(data, 4);
+    data->data[data->length++] = (val >>  0) & 0xff;
+    data->data[data->length++] = (val >>  8) & 0xff;
+    data->data[data->length++] = (val >> 16) & 0xff;
+    data->data[data->length++] = (val >> 24) & 0xff;
+    data->data[data->length++] = (val >> 32) & 0xff;
+    data->data[data->length++] = (val >> 40) & 0xff;
+    data->data[data->length++] = (val >> 48) & 0xff;
+    data->data[data->length++] = (val >> 54) & 0xff;
+}
+
+static void usb_mtp_add_u16_array(MTPData *data, uint32_t len,
+                                  const uint16_t *vals)
+{
+    int i;
+
+    usb_mtp_add_u32(data, len);
+    for (i = 0; i < len; i++) {
+        usb_mtp_add_u16(data, vals[i]);
+    }
+}
+
+static void usb_mtp_add_u32_array(MTPData *data, uint32_t len,
+                                  const uint32_t *vals)
+{
+    int i;
+
+    usb_mtp_add_u32(data, len);
+    for (i = 0; i < len; i++) {
+        usb_mtp_add_u32(data, vals[i]);
+    }
+}
+
+static void usb_mtp_add_wstr(MTPData *data, const wchar_t *str)
+{
+    uint32_t len = wcslen(str);
+    int i;
+
+    if (len > 0) {
+        len++; /* include terminating L'\0' */
+    }
+
+    usb_mtp_add_u8(data, len);
+    for (i = 0; i < len; i++) {
+        usb_mtp_add_u16(data, str[i]);
+    }
+}
+
+static void usb_mtp_add_str(MTPData *data, const char *str)
+{
+    uint32_t len = strlen(str)+1;
+    wchar_t wstr[len];
+    size_t ret;
+
+    ret = mbstowcs(wstr, str, len);
+    if (ret == -1) {
+        usb_mtp_add_wstr(data, L"Oops");
+    } else {
+        usb_mtp_add_wstr(data, wstr);
+    }
+}
+
+static void usb_mtp_add_time(MTPData *data, time_t time)
+{
+    char buf[16];
+    struct tm tm;
+
+    gmtime_r(&time, &tm);
+    strftime(buf, sizeof(buf), "%Y%m%dT%H%M%S", &tm);
+    usb_mtp_add_str(data, buf);
+}
+
+/* ----------------------------------------------------------------------- */
+
+static void usb_mtp_queue_result(MTPState *s, uint16_t code, uint32_t trans,
+                                 int argc, uint32_t arg0, uint32_t arg1)
+{
+    MTPControl *c = g_new0(MTPControl, 1);
+
+    c->code  = code;
+    c->trans = trans;
+    c->argc  = argc;
+    if (argc > 0) {
+        c->argv[0] = arg0;
+    }
+    if (argc > 1) {
+        c->argv[1] = arg1;
+    }
+
+    assert(s->result == NULL);
+    s->result = c;
+}
+
+/* ----------------------------------------------------------------------- */
+
+static MTPData *usb_mtp_get_device_info(MTPState *s, MTPControl *c)
+{
+    static const uint16_t ops[] = {
+        CMD_GET_DEVICE_INFO,
+        CMD_OPEN_SESSION,
+        CMD_CLOSE_SESSION,
+        CMD_GET_STORAGE_IDS,
+        CMD_GET_STORAGE_INFO,
+        CMD_GET_NUM_OBJECTS,
+        CMD_GET_OBJECT_HANDLES,
+        CMD_GET_OBJECT_INFO,
+        CMD_GET_OBJECT,
+        CMD_GET_PARTIAL_OBJECT,
+    };
+    static const uint16_t fmt[] = {
+        FMT_UNDEFINED_OBJECT,
+        FMT_ASSOCIATION,
+    };
+    MTPData *d = usb_mtp_data_alloc(c);
+
+    trace_usb_mtp_op_get_device_info(s->dev.addr);
+
+    usb_mtp_add_u16(d, 0x0100);
+    usb_mtp_add_u32(d, 0xffffffff);
+    usb_mtp_add_u16(d, 0x0101);
+    usb_mtp_add_wstr(d, L"");
+    usb_mtp_add_u16(d, 0x0000);
+
+    usb_mtp_add_u16_array(d, ARRAY_SIZE(ops), ops);
+    usb_mtp_add_u16_array(d, 0, NULL);
+    usb_mtp_add_u16_array(d, 0, NULL);
+    usb_mtp_add_u16_array(d, 0, NULL);
+    usb_mtp_add_u16_array(d, ARRAY_SIZE(fmt), fmt);
+
+    usb_mtp_add_wstr(d, L"" MTP_MANUFACTURER);
+    usb_mtp_add_wstr(d, L"" MTP_PRODUCT);
+    usb_mtp_add_wstr(d, L"0.1");
+    usb_mtp_add_wstr(d, L"123456789abcdef123456789abcdef");
+
+    return d;
+}
+
+static MTPData *usb_mtp_get_storage_ids(MTPState *s, MTPControl *c)
+{
+    static const uint32_t ids[] = {
+        QEMU_STORAGE_ID,
+    };
+    MTPData *d = usb_mtp_data_alloc(c);
+
+    trace_usb_mtp_op_get_storage_ids(s->dev.addr);
+
+    usb_mtp_add_u32_array(d, ARRAY_SIZE(ids), ids);
+
+    return d;
+}
+
+static MTPData *usb_mtp_get_storage_info(MTPState *s, MTPControl *c)
+{
+    MTPData *d = usb_mtp_data_alloc(c);
+    struct statvfs buf;
+    int rc;
+
+    trace_usb_mtp_op_get_storage_info(s->dev.addr);
+
+    if (FLAG_SET(s, MTP_FLAG_WRITABLE)) {
+        usb_mtp_add_u16(d, 0x0003);
+        usb_mtp_add_u16(d, 0x0002);
+        usb_mtp_add_u16(d, 0x0000);
+    } else {
+        usb_mtp_add_u16(d, 0x0001);
+        usb_mtp_add_u16(d, 0x0002);
+        usb_mtp_add_u16(d, 0x0001);
+    }
+
+    rc = statvfs(s->root, &buf);
+    if (rc == 0) {
+        usb_mtp_add_u64(d, (uint64_t)buf.f_frsize * buf.f_blocks);
+        usb_mtp_add_u64(d, (uint64_t)buf.f_bavail * buf.f_blocks);
+        usb_mtp_add_u32(d, buf.f_ffree);
+    } else {
+        usb_mtp_add_u64(d, 0xffffffff);
+        usb_mtp_add_u64(d, 0xffffffff);
+        usb_mtp_add_u32(d, 0xffffffff);
+    }
+
+    usb_mtp_add_str(d, s->desc);
+    usb_mtp_add_wstr(d, L"123456789abcdef");
+    return d;
+}
+
+static MTPData *usb_mtp_get_object_handles(MTPState *s, MTPControl *c,
+                                           MTPObject *o)
+{
+    MTPData *d = usb_mtp_data_alloc(c);
+    uint32_t i, handles[o->nchildren];
+
+    trace_usb_mtp_op_get_object_handles(s->dev.addr, o->handle, o->path);
+
+    for (i = 0; i < o->nchildren; i++) {
+        handles[i] = o->children[i]->handle;
+    }
+    usb_mtp_add_u32_array(d, o->nchildren, handles);
+
+    return d;
+}
+
+static MTPData *usb_mtp_get_object_info(MTPState *s, MTPControl *c,
+                                        MTPObject *o)
+{
+    MTPData *d = usb_mtp_data_alloc(c);
+
+    trace_usb_mtp_op_get_object_info(s->dev.addr, o->handle, o->path);
+
+    usb_mtp_add_u32(d, QEMU_STORAGE_ID);
+    usb_mtp_add_u16(d, o->format);
+    usb_mtp_add_u16(d, 0);
+    usb_mtp_add_u32(d, o->stat.st_size);
+
+    usb_mtp_add_u16(d, 0);
+    usb_mtp_add_u32(d, 0);
+    usb_mtp_add_u32(d, 0);
+    usb_mtp_add_u32(d, 0);
+    usb_mtp_add_u32(d, 0);
+    usb_mtp_add_u32(d, 0);
+    usb_mtp_add_u32(d, 0);
+
+    if (o->parent) {
+        usb_mtp_add_u32(d, o->parent->handle);
+    } else {
+        usb_mtp_add_u32(d, 0);
+    }
+    if (o->format == FMT_ASSOCIATION) {
+        usb_mtp_add_u16(d, 0x0001);
+        usb_mtp_add_u32(d, 0x00000001);
+        usb_mtp_add_u32(d, 0);
+    } else {
+        usb_mtp_add_u16(d, 0);
+        usb_mtp_add_u32(d, 0);
+        usb_mtp_add_u32(d, 0);
+    }
+
+    usb_mtp_add_str(d, o->name);
+    usb_mtp_add_time(d, o->stat.st_ctime);
+    usb_mtp_add_time(d, o->stat.st_mtime);
+    usb_mtp_add_wstr(d, L"");
+
+    return d;
+}
+
+static MTPData *usb_mtp_get_object(MTPState *s, MTPControl *c,
+                                   MTPObject *o)
+{
+    MTPData *d = usb_mtp_data_alloc(c);
+
+    trace_usb_mtp_op_get_object(s->dev.addr, o->handle, o->path);
+
+    d->fd = open(o->path, O_RDONLY);
+    if (d->fd == -1) {
+        return NULL;
+    }
+    d->length = o->stat.st_size;
+    d->alloc  = 512;
+    d->data   = g_malloc(d->alloc);
+    return d;
+}
+
+static MTPData *usb_mtp_get_partial_object(MTPState *s, MTPControl *c,
+                                           MTPObject *o)
+{
+    MTPData *d = usb_mtp_data_alloc(c);
+    off_t offset;
+
+    trace_usb_mtp_op_get_partial_object(s->dev.addr, o->handle, o->path,
+                                        c->argv[1], c->argv[2]);
+
+    d->fd = open(o->path, O_RDONLY);
+    if (d->fd == -1) {
+        return NULL;
+    }
+
+    offset = c->argv[1];
+    if (offset > o->stat.st_size) {
+        offset = o->stat.st_size;
+    }
+    lseek(d->fd, offset, SEEK_SET);
+
+    d->length = c->argv[2];
+    if (d->length > o->stat.st_size - offset) {
+        d->length = o->stat.st_size - offset;
+    }
+
+    return d;
+}
+
+static void usb_mtp_command(MTPState *s, MTPControl *c)
+{
+    MTPData *data_in = NULL;
+    MTPObject *o;
+    uint32_t nres = 0, res0 = 0;
+
+    /* sanity checks */
+    if (c->code >= CMD_CLOSE_SESSION && s->session == 0) {
+        usb_mtp_queue_result(s, RES_SESSION_NOT_OPEN,
+                             c->trans, 0, 0, 0);
+        return;
+    }
+
+    /* process commands */
+    switch (c->code) {
+    case CMD_GET_DEVICE_INFO:
+        data_in = usb_mtp_get_device_info(s, c);
+        break;
+    case CMD_OPEN_SESSION:
+        if (s->session) {
+            usb_mtp_queue_result(s, RES_SESSION_ALREADY_OPEN,
+                                 c->trans, 1, s->session, 0);
+            return;
+        }
+        if (c->argv[0] == 0) {
+            usb_mtp_queue_result(s, RES_INVALID_PARAMETER,
+                                 c->trans, 0, 0, 0);
+            return;
+        }
+        trace_usb_mtp_op_open_session(s->dev.addr);
+        s->session = c->argv[0];
+        usb_mtp_object_alloc(s, s->next_handle++, NULL, s->root);
+        break;
+    case CMD_CLOSE_SESSION:
+        trace_usb_mtp_op_close_session(s->dev.addr);
+        s->session = 0;
+        s->next_handle = 0;
+        usb_mtp_object_free(s, QTAILQ_FIRST(&s->objects));
+        assert(QTAILQ_EMPTY(&s->objects));
+        break;
+    case CMD_GET_STORAGE_IDS:
+        data_in = usb_mtp_get_storage_ids(s, c);
+        break;
+    case CMD_GET_STORAGE_INFO:
+        if (c->argv[0] != QEMU_STORAGE_ID &&
+            c->argv[0] != 0xffffffff) {
+            usb_mtp_queue_result(s, RES_INVALID_STORAGE_ID,
+                                 c->trans, 0, 0, 0);
+            return;
+        }
+        data_in = usb_mtp_get_storage_info(s, c);
+        break;
+    case CMD_GET_NUM_OBJECTS:
+    case CMD_GET_OBJECT_HANDLES:
+        if (c->argv[0] != QEMU_STORAGE_ID &&
+            c->argv[0] != 0xffffffff) {
+            usb_mtp_queue_result(s, RES_INVALID_STORAGE_ID,
+                                 c->trans, 0, 0, 0);
+            return;
+        }
+        if (c->argv[1] != 0x00000000) {
+            usb_mtp_queue_result(s, RES_SPEC_BY_FORMAT_UNSUPPORTED,
+                                 c->trans, 0, 0, 0);
+            return;
+        }
+        if (c->argv[2] == 0x00000000 ||
+            c->argv[2] == 0xffffffff) {
+            o = QTAILQ_FIRST(&s->objects);
+        } else {
+            o = usb_mtp_object_lookup(s, c->argv[2]);
+        }
+        if (o == NULL) {
+            usb_mtp_queue_result(s, RES_INVALID_OBJECT_HANDLE,
+                                 c->trans, 0, 0, 0);
+            return;
+        }
+        if (o->format != FMT_ASSOCIATION) {
+            usb_mtp_queue_result(s, RES_INVALID_PARENT_OBJECT,
+                                 c->trans, 0, 0, 0);
+            return;
+        }
+        if (o->nchildren == -1) {
+            usb_mtp_object_readdir(s, o);
+        }
+        if (c->code == CMD_GET_NUM_OBJECTS) {
+            trace_usb_mtp_op_get_num_objects(s->dev.addr, o->handle, o->path);
+            nres = 1;
+            res0 = o->nchildren;
+        } else {
+            data_in = usb_mtp_get_object_handles(s, c, o);
+        }
+        break;
+    case CMD_GET_OBJECT_INFO:
+        o = usb_mtp_object_lookup(s, c->argv[0]);
+        if (o == NULL) {
+            usb_mtp_queue_result(s, RES_INVALID_OBJECT_HANDLE,
+                                 c->trans, 0, 0, 0);
+            return;
+        }
+        data_in = usb_mtp_get_object_info(s, c, o);
+        break;
+    case CMD_GET_OBJECT:
+        o = usb_mtp_object_lookup(s, c->argv[0]);
+        if (o == NULL) {
+            usb_mtp_queue_result(s, RES_INVALID_OBJECT_HANDLE,
+                                 c->trans, 0, 0, 0);
+            return;
+        }
+        if (o->format == FMT_ASSOCIATION) {
+            usb_mtp_queue_result(s, RES_INVALID_OBJECT_HANDLE,
+                                 c->trans, 0, 0, 0);
+            return;
+        }
+        data_in = usb_mtp_get_object(s, c, o);
+        if (NULL == data_in) {
+            fprintf(stderr, "%s: TODO: handle error\n", __func__);
+        }
+        break;
+    case CMD_GET_PARTIAL_OBJECT:
+        o = usb_mtp_object_lookup(s, c->argv[0]);
+        if (o == NULL) {
+            usb_mtp_queue_result(s, RES_INVALID_OBJECT_HANDLE,
+                                 c->trans, 0, 0, 0);
+            return;
+        }
+        if (o->format == FMT_ASSOCIATION) {
+            usb_mtp_queue_result(s, RES_INVALID_OBJECT_HANDLE,
+                                 c->trans, 0, 0, 0);
+            return;
+        }
+        data_in = usb_mtp_get_partial_object(s, c, o);
+        if (NULL == data_in) {
+            fprintf(stderr, "%s: TODO: handle error\n", __func__);
+        }
+        nres = 1;
+        res0 = data_in->length;
+        break;
+    default:
+        fprintf(stderr, "%s: unknown command code 0x%04x\n",
+                __func__, c->code);
+        usb_mtp_queue_result(s, RES_OPERATION_NOT_SUPPORTED,
+                             c->trans, 0, 0, 0);
+        return;
+    }
+
+    /* return results on success */
+    if (data_in) {
+        assert(s->data_in == NULL);
+        s->data_in = data_in;
+    }
+    usb_mtp_queue_result(s, RES_OK, c->trans, nres, res0, 0);
+}
+
+/* ----------------------------------------------------------------------- */
+
+static void usb_mtp_handle_reset(USBDevice *dev)
+{
+    MTPState *s = DO_UPCAST(MTPState, dev, dev);
+
+    trace_usb_mtp_reset(s->dev.addr);
+
+    s->session = 0;
+    usb_mtp_data_free(s->data_in);
+    s->data_in = NULL;
+    usb_mtp_data_free(s->data_out);
+    s->data_out = NULL;
+    g_free(s->result);
+    s->result = NULL;
+}
+
+static void usb_mtp_handle_control(USBDevice *dev, USBPacket *p,
+                                   int request, int value, int index,
+                                   int length, uint8_t *data)
+{
+    int ret;
+
+    ret = usb_desc_handle_control(dev, p, request, value, index, length, data);
+    if (ret >= 0) {
+        return;
+    }
+
+    trace_usb_mtp_stall(dev->addr, "unknown control request");
+    p->status = USB_RET_STALL;
+}
+
+static void usb_mtp_cancel_packet(USBDevice *dev, USBPacket *p)
+{
+    fprintf(stderr, "%s\n", __func__);
+}
+
+static void usb_mtp_handle_data(USBDevice *dev, USBPacket *p)
+{
+    MTPState *s = DO_UPCAST(MTPState, dev, dev);
+    MTPControl cmd;
+    mtp_container container;
+    uint32_t params[5];
+    int i, rc;
+
+    switch (p->ep->nr) {
+    case EP_DATA_IN:
+        if (s->data_out != NULL) {
+            /* guest bug */
+            trace_usb_mtp_stall(s->dev.addr, "awaiting data-out");
+            p->status = USB_RET_STALL;
+            return;
+        }
+        if (p->iov.size < sizeof(container)) {
+            trace_usb_mtp_stall(s->dev.addr, "packet too small");
+            p->status = USB_RET_STALL;
+            return;
+        }
+        if (s->data_in !=  NULL) {
+            MTPData *d = s->data_in;
+            int dlen = d->length - d->offset;
+            if (d->first) {
+                trace_usb_mtp_data_in(s->dev.addr, d->trans, d->length);
+                container.length = cpu_to_le32(d->length + sizeof(container));
+                container.type   = cpu_to_le16(TYPE_DATA);
+                container.code   = cpu_to_le16(d->code);
+                container.trans  = cpu_to_le32(d->trans);
+                usb_packet_copy(p, &container, sizeof(container));
+                d->first = false;
+                if (dlen > p->iov.size - sizeof(container)) {
+                    dlen = p->iov.size - sizeof(container);
+                }
+            } else {
+                if (dlen > p->iov.size) {
+                    dlen = p->iov.size;
+                }
+            }
+            if (d->fd == -1) {
+                usb_packet_copy(p, d->data + d->offset, dlen);
+            } else {
+                if (d->alloc < p->iov.size) {
+                    d->alloc = p->iov.size;
+                    d->data = g_realloc(d->data, d->alloc);
+                }
+                rc = read(d->fd, d->data, dlen);
+                if (rc != dlen) {
+                    fprintf(stderr, "%s: TODO: handle read error\n", __func__);
+                }
+                usb_packet_copy(p, d->data, dlen);
+            }
+            d->offset += dlen;
+            if (d->offset == d->length) {
+                usb_mtp_data_free(s->data_in);
+                s->data_in = NULL;
+            }
+        } else if (s->result != NULL) {
+            MTPControl *r = s->result;
+            int length = sizeof(container) + r->argc * sizeof(uint32_t);
+            if (r->code == RES_OK) {
+                trace_usb_mtp_success(s->dev.addr, r->trans,
+                                      (r->argc > 0) ? r->argv[0] : 0,
+                                      (r->argc > 1) ? r->argv[1] : 0);
+            } else {
+                trace_usb_mtp_error(s->dev.addr, r->code, r->trans,
+                                    (r->argc > 0) ? r->argv[0] : 0,
+                                    (r->argc > 1) ? r->argv[1] : 0);
+            }
+            container.length = cpu_to_le32(length);
+            container.type   = cpu_to_le16(TYPE_RESPONSE);
+            container.code   = cpu_to_le16(r->code);
+            container.trans  = cpu_to_le32(r->trans);
+            for (i = 0; i < r->argc; i++) {
+                params[i] = cpu_to_le32(r->argv[i]);
+            }
+            usb_packet_copy(p, &container, sizeof(container));
+            usb_packet_copy(p, &params, length - sizeof(container));
+            g_free(s->result);
+            s->result = NULL;
+        }
+        break;
+    case EP_DATA_OUT:
+        if (p->iov.size < sizeof(container)) {
+            trace_usb_mtp_stall(s->dev.addr, "packet too small");
+            p->status = USB_RET_STALL;
+            return;
+        }
+        usb_packet_copy(p, &container, sizeof(container));
+        switch (le16_to_cpu(container.type)) {
+        case TYPE_COMMAND:
+            if (s->data_in || s->data_out || s->result) {
+                trace_usb_mtp_stall(s->dev.addr, "transaction inflight");
+                p->status = USB_RET_STALL;
+                return;
+            }
+            cmd.code = le16_to_cpu(container.code);
+            cmd.argc = (le32_to_cpu(container.length) - sizeof(container))
+                / sizeof(uint32_t);
+            cmd.trans = le32_to_cpu(container.trans);
+            usb_packet_copy(p, &params, cmd.argc * sizeof(uint32_t));
+            for (i = 0; i < cmd.argc; i++) {
+                cmd.argv[i] = le32_to_cpu(params[i]);
+            }
+            trace_usb_mtp_command(s->dev.addr, cmd.code, cmd.trans,
+                                  (cmd.argc > 0) ? cmd.argv[0] : 0,
+                                  (cmd.argc > 1) ? cmd.argv[1] : 0,
+                                  (cmd.argc > 2) ? cmd.argv[2] : 0,
+                                  (cmd.argc > 3) ? cmd.argv[3] : 0,
+                                  (cmd.argc > 4) ? cmd.argv[4] : 0);
+            usb_mtp_command(s, &cmd);
+            break;
+        default:
+            iov_hexdump(p->iov.iov, p->iov.niov, stderr, "mtp-out", 32);
+            trace_usb_mtp_stall(s->dev.addr, "TODO: implement data-out");
+            p->status = USB_RET_STALL;
+            return;
+        }
+        break;
+    case EP_EVENT:
+        p->status = USB_RET_NAK;
+        return;
+    default:
+        trace_usb_mtp_stall(s->dev.addr, "invalid endpoint");
+        p->status = USB_RET_STALL;
+        return;
+    }
+
+    if (p->actual_length == 0) {
+        trace_usb_mtp_nak(s->dev.addr, p->ep->nr);
+        p->status = USB_RET_NAK;
+        return;
+    } else {
+        trace_usb_mtp_xfer(s->dev.addr, p->ep->nr, p->actual_length,
+                           p->iov.size);
+        return;
+    }
+}
+
+static int usb_mtp_initfn(USBDevice *dev)
+{
+    MTPState *s = DO_UPCAST(MTPState, dev, dev);
+
+    usb_desc_create_serial(dev);
+    usb_desc_init(dev);
+    QTAILQ_INIT(&s->objects);
+    if (s->desc == NULL) {
+        s->desc = strrchr(s->root, '/');
+        if (s->desc) {
+            s->desc = g_strdup(s->desc + 1);
+        } else {
+            s->desc = g_strdup("none");
+        }
+    }
+    return 0;
+}
+
+static const VMStateDescription vmstate_usb_mtp = {
+    .name = "usb-mtp",
+    .unmigratable = 1,
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .fields = (VMStateField[]) {
+        VMSTATE_USB_DEVICE(dev, MTPState),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
+static Property mtp_properties[] = {
+    DEFINE_PROP_STRING("root", MTPState, root),
+    DEFINE_PROP_STRING("desc", MTPState, desc),
+    DEFINE_PROP_END_OF_LIST(),
+};
+
+static void usb_mtp_class_initfn(ObjectClass *klass, void *data)
+{
+    DeviceClass *dc = DEVICE_CLASS(klass);
+    USBDeviceClass *uc = USB_DEVICE_CLASS(klass);
+
+    uc->init           = usb_mtp_initfn;
+    uc->product_desc   = "QEMU USB MTP";
+    uc->usb_desc       = &desc;
+    uc->cancel_packet  = usb_mtp_cancel_packet;
+    uc->handle_attach  = usb_desc_attach;
+    uc->handle_reset   = usb_mtp_handle_reset;
+    uc->handle_control = usb_mtp_handle_control;
+    uc->handle_data    = usb_mtp_handle_data;
+    dc->fw_name = "mtp";
+    dc->vmsd = &vmstate_usb_mtp;
+    dc->props = mtp_properties;
+}
+
+static TypeInfo mtp_info = {
+    .name          = "usb-mtp",
+    .parent        = TYPE_USB_DEVICE,
+    .instance_size = sizeof(MTPState),
+    .class_init    = usb_mtp_class_initfn,
+};
+
+static void usb_mtp_register_types(void)
+{
+    type_register_static(&mtp_info);
+}
+
+type_init(usb_mtp_register_types)