See the "INSTALL" file.
libmtp implements an MTP initiator, which means it initiate MTP sessions with devices. The devices responding are known as MTP responders. libmtp runs on something with a USB host controller interface, using libusb to access the host controller.
If you're more interested in the MTP responders, gadgets like MP3 players, mobile phones etc, look into MeeGo:s Buteo Sync: http://wiki.meego.com/Buteo - these guys are creating a fully open source MTP responder.
libmtp is based on several ancestors:
libptp2 by Mariusz Woloszyn was the starting point used by Richard A. Low for the initial starter port. You can find it at http://libptp.sourceforge.net/
libgphoto2 by Mariusz Woloszyn and Marcus Meissner was used at a later stage since it was (is) more actively maintained. libmtp tracks the PTP implementation in libgphoto2 and considers it an upstream project. We will try to submit anything generally useful back to libgphoto2 and not make double efforts. In practice this means we use ptp.c, ptp.h and ptp-pack.c verbatim from the libgphoto2 source code. If you need to change things in these files, make sure it is so general that libgphoto2 will want to merge it to their codebase too. You find libgphoto2 as part of gPhoto: http://gphoto.sourceforge.net/
libnjb was a project that Richard and Linus were working on before libmtp. When Linus took Richards initial port and made an generic C API he re-used the philosophy and much code from libnjb. Many of the sample programs are for example taken quite literally from libnjb. You find it here: http://libnjb.sourceforge.net/
See the project page at http://libmtp.sourceforge.net/ We always need your help. There is a mailinglist and a bug report system there.
People who want to discuss MTP devices in fora seem to hang out on the forums at AnythingbutiPod: http://www.anythingbutipod.com/forum/
libmtp has support for the pkg-config script by adding a libmtp.pc entry in $(prefix)/lib/pkgconfig. To compile a libmtp program, "just" write:
gcc -o foo pkg-config --cflags --libs libmtp foo.c
This also simplifies compilation using autoconf and pkg-config: just write e.g.
PKG_CHECK_MODULES(MTP, libmtp) AC_SUBST(MTP_CFLAGS) AC_SUBST(MTP_LIBS)
To have libmtp LIBS and CFLAGS defined. Needless to say, this will only work if you have pkgconfig installed on your system, but most people have nowadays.
If your library is installed in e.g. /usr/local you may have to tell this to pkgconfig by setting the PKG_CONFIG_PATH thus:
export PKG_CONFIG_PATH=/usr/local/lib/pkgconfig
Read the API documentation that can be generated with doxygen. It will be output in doc/html if you have Doxygen properly installed. (It will not be created unless you have Doxygen!)
For information about the Media Transfer Protocol, see: http://en.wikipedia.org/wiki/Media_Transfer_Protocol
The official 1.0 specification for MTP was released by the USB Implementers Forum in may, 2008. Prior to this, only a proprietary Microsoft version was available, and quite a few devices out there still use some aspects of the Microsoft version, which deviates from the specified standard. You can find the official specification here: http://www.usb.org/developers/devclass_docs/MTP_1.0.zip
In the subdirectory "examples" you find a number of command-line tools, illustrating the use of libmtp in very simple terms.
Please do not complain about the usability or documentation of these examples, they look like they do for two reasons:
They are examples, not tools. If they were intended for day-to-day usage by commandline freaks, I would have called them "tools" not "examples".
The MTP usage paradigm is that a daemon should hook the device upon connection, and that it should be released by unplugging. GUI tools utilizing HAL (hald) and D-Bus do this much better than any commandline program ever can. (See below on bugs.) Specificationwise this is a bug, however it is present in many, many devices.
That said, if you want to pick up and maintain the examples, please volunteer.
Some MTP devices have strange pecularities. We try to work around these whenever we can, sometimes we cannot work around it or we cannot test your solution.
mtp-* tools doesn't work because someone else is already hogging the device
This is a common problem, the most common case could be that gphoto2 (which can also talk PTP/MTP) is taking over the device as soon as it's plugged in. Some distributions are configured that way. Counter it like this:
gvfs-mount -s gphoto2
Then re-attach the device.
Sometimes the "gvfs-gphoto2-volume-monitor" is running on the system and hogging the device, try something like:
pkill gfvs-gphoto2-volume-monitor
Then plug in the device and issue "mtp-detect" to figure out if this may be the case.
Generic MTP/PTP disconnect misbehaviour: we have noticed that Windows Media Player apparently never close the session to an MTP device. There is a daemon in Windows that "hooks" the device by opening a PTP session to any MTP device, whenever it is plugged in. This daemon proxies any subsequent transactions to/from the device and will never close the session, thus Windows simply does not close sessions at all.
For example this means that a device may work the first time you run some command-line example like "mtp-detect" while subsequent runs fail.
Typical sign of this illness: broken pipes on closing sessions, on the main transfer pipes(s) or the interrupt pipe:
Closing session usb_clear_halt() on INTERRUPT endpoint: Broken pipe OK.
This means that device manufacturers doesn't notice any problems with devices that do not correctly handle closing PTP/MTP sessions, since Windows never do it. The proper way of closing a session in Windows is to unplug the device, simply put.
Since libmtp actually tries to close sessions, some devices may fail since the close session functionality has never been properly tested, and "it works with Windows" is sort of the testing criteria at some companies.
You can get Windows-like behaviour on Linux by running a udev-aware libmtp GUI client like Rhythmbox or Gnomad2, which will "hook" the device when you plug it in, and "release" it if you unplug it, and you start/end you transfer sessions by plugging/unplugging the USB cable.
The "Unix way" of running small programs that open the device, do something, then close the device, isn't really working with such devices and you cannot expect to have command line tools like the mtp examples work with them. You could implement new example programs that just call to a mediating daemon like the Windows MTP stack does. (And change all programs using libmtp directly today.)
If this bug in your device annoys you, contact your device manufacturer and ask them to test their product with some libmtp program.
Android locked screen: some devices just report zero files and no storages when the device is locked, probably so as not to allow the MTP access to be used as a "backdoor" into the device. Unlock the device before listing files, set the autolock to some large value or disabled if it disturbs you, you are causing this to yourself.
Samsung Android 2.3.x devices: these have a special MTP stack with some specific bugs that we have maybe nailed down now. It suffers from an "immediate connect" syndrome, i.e. you have to connect to the device within 7 seconds of plugging in, or it will go numb. This also goes for command-line activity with the example programs, so this device is better used with a GUI tool like Rhythmbox, gnomad2...
Generic USB misbehaviour: some devices behave badly under MTP and USB mass storage alike, even down to the lowest layers of USB. You can always discuss such issues at the linux-usb mailing list if you're using Linux: http://www.linux-usb.org/mailing.html
If you have a problem specific to USB mass storage mode, there is a list of strange behaving devices in the Linux kernel: http://lxr.linux.no/linux/drivers/usb/storage/unusual_devs.h You can discuss this too on the mentioned list, for understanding the quirks, see: http://www2.one-eyed-alien.net/~mdharm/linux-usb/target_offenses.txt
Generic certificate misbehaviour. All devices are actually required to support a device certificate to be able to encrypt Windows Media (WMA/WMV) files. However there are obviously a lot of devices out there which doesn't support this at all but instead crash. Typical printout:
Error 2: PTP Layer error 02ff: get_device_unicode_property(): failed to get unicode property.
This should only affect "mtp-detect", there is no other application currently retrieveing the certificate (not that we know anyway).
Kernel bug on Linux. Linux 2.6.16 is generally speaking required to use any MTP device under USB 2.0. This is because the EHCI driver previously did not support zero-length writes to endpoints. It should work in most cases however, or if you connect it to an UHCI/OHCI port instead (yielding lower speed). But please just use a recent kernel.
Zen models AVI file seeking problem: the Zens cannot parse the files for the runlength metadata. Do not transfer file with e.g. mtp-sendfile, use mtp-sendtr and set the length of the track to the apropriate number of seconds and it will work. In graphical clients, use a "track transfer" function to send these AVI files, the Zens need the metadata associated with tracks to play back movies properly. Movies are considered "tracks" in the MTP world.
Some devices that disregard the metadata sent with the MTP commands will parse the files for e.g. ID3 metadata. Some still of these devices expect only ID3v2.3 metadata and will fail with a modern ID3v2,4 tag writer, like many of those found in Linux applications. Windows Media Player use ID3v2.3 only, so many manufacturers only test this version.
The Zen Vision:M (possibly more Creative Zens) has a firmware bug that makes it drop the last two characters off a playlist name. It is fixed in later firmware.
For Creative Technology devices, there are hard limits on how many files can be put onto the device. For a 30 GiB device (like the Zen Xtra) the limit is 6000, for a 60 GiB device the limit is 15000 files. For further Creative pecularities, see the FAQ sections at www.nomadness.net.
Sandisk sansa c150 and probably several other Sandisk devices (and possibly devices from other manufacturers) have a dual mode with MTP and USB mass storage. The device will initially claim to be mass storage so udev will capture is and make the use of MTP mode impossible. One way of avoiding it could be to be to blacklist the "usb-storage" module in /etc/modprobe.c/blacklist with a row like this: "blacklist usb-storage". Some have even removed the "usb-storage.ko" (kernel module file) to avoid loading.
Sandisk Sansa Fuze has three modes: auto, MTP or mass storage (MSC). Please set it to MTP to avoid problems with libmtp.
The iriver devices (possibly all of them) cannot handle the enhanced GetObjectPropList MTP command (0x9805) properly. So they have been banned from using it.
iriver devices have problems with older versions of libmtp and with new devices libmtp does not know of as of yet, since it has an oldstyle USB device controller that cannot handle zero writes. (Register your device with us!) All their devices are likely to need a special device flag in the src/libusb-glue.c database.
The Samsung Yepp T9 has several strange characteristics, some that we've managed to work around. (For example it will return multiple PTP packages in a single transaction.)
The early firmware for Philips HDD players is known to be problematic. Please upgrade to as new firmware as you can get. (Yes this requires some kind of Windows Installation I think.)
Philips HDD 1630/16 or 1630/17 etc may lock themselves up, turning inresponsive due to internal corruption. This typically gives an error in opening the PTP session. Apparently you can do a "repair" with the firmware utility (Windows only) which will often fix this problem and make the device responsive again.
Some devices that implement GetObjectPropList (0x9805) will not return the entire object list if you request a list for object 0xffffffffu. (But they should.) So they may need the special DEVICE_FLAG_BROKEN_MTPGETOBJPROPLIST_ALL.
Some (smaller) subset of devices cannot even get all the properties for a single object in one go, these need the DEVICE_FLAG_BROKEN_MTPGETOBJPROPLIST. Currently only the iriver devices seem to have this bug.
The Toshiba Gigabeat S (and probably its sibling the Microsoft Zune and other Toshiba devices) will only display album information tags for a song in case there is also an abstract album (created with the album interface) with the exact same name.
The Zen Vision:M has an older firmware which is very corrupt, it is incompatible with the Linux USB stack altogether. The kernel dmesg will look something like this, and you have to upgrade the firmware using Windows: usb 4-5: new high speed USB device using ehci_hcd and address 5 usb 4-5: configuration #1 chosen from 1 choice usb 4-5: can't set config #1, error -110
The Sirus Stiletto does not seem to allow you to copy any files off the device. This may be someone's idea of copy protection.
The Samsung P2 assigns parent folder ID 0 to all unknown file types.(i.e. moves them to the root folder)
The Sandisk Sansa Clip+ needs a firmware upgrade in earlier versions in order to work properly.
If you happen upon a device which libmtp claims it cannot autodetect, please submit the vendor ID and device ID (these can be obtained from the "lsusb" and "lsusb -n" commands run as root) as a bug, patch or feature request on the Sourceforge bug tracker at our homepage. If it gives a sensible output from "mtp-detect" then please attach the result as well as it teach us some stuff about your device. If you've done some additional hacking, join our mailinglist and post your experiences there.
If you want to be able to hack some more and you're not afraid of C hacking, add an entry for your device's vendor/product ID and a descriptive string to the database in the file src/music-players.h.
If you want to poke around to see if your device has some special pecularities, you can test some special device flags (defined in src/device-flags.h) by inserting them together with your device entry in src/music-players.h. Flags can be tested in isolation or catenated with "|" (binary OR). If relatives to your device use a certain flag, chances are high that a new device will need it too, typically from the same manufacturer.
The most common flag that needs to be set is the DEVICE_FLAG_UNLOAD_DRIVER that detach any Linux kernel drivers that may have attached to the device making MTP access impossible. This is however not expected to really work: this is a problem being tracked as of now (2007-08-04). See the "last resort" solutions below if you really need to get your dual-mode device to work with MTP.
Another flag which is easy to identify is the DEVICE_FLAG_NO_ZERO_READS, which remedies connection timeouts when getting files, and some timeouts on e.g. successive "mtp-connect" calls.
If your device is very problematic we are curious of how it works under Windows, so we enjoy reading USB packet sniffs that reveal the low-level traffic carried out between Windows Media Player and your device. This can be done using e.g.:
The trial version of HHD Softwares software-only USB monitor. You need to get a copy of version 2.37 since the newer trial versions won't let you carry out the needed packet sniffs. (As of 2007-03-10 a copy can be found at: http://www.cobbleware.com/files/usb-monitor-237.exe)
There are other USB monitors as well, some more expensive alternatives use hardware and even measure electronic characteristics of the traffic (which is far too much detail for us).
Device sniffs are an easy read since the PTP/MTP protocol is nicely structured. All commands will have a structure such as this in the log, we examplify with a object list request:
PTP REQEUST: 000120: Bulk or Interrupt Transfer (UP), 03.09.2007 12:49:25.9843750 +0.0 Pipe Handle: 0x863ce234 (Endpoint Address: 0x2) Send 0x20 bytes to the device: 20 00 00 00 01 00 05 98 23 00 00 00 27 03 00 10 ......?#...'... Length TYPE CMD Trans# Param1
00 00 00 00 02 DC 00 00 00 00 00 00 00 00 00 00 .....Ü.......... Param2 Param3 Param4 Param5
[OPTIONAL] DATA PHASE: 000121: Bulk or Interrupt Transfer (UP), 03.09.2007 12:49:26.0 +0.0156250 Pipe Handle: 0x863ce214 (Endpoint Address: 0x81) Get 0x1a bytes from the device: 1A 00 00 00 02 00 05 98 23 00 00 00 01 00 00 00 .......?#....... Length TYPE CMD Trans# DATA
27 03 00 10 02 DC 04 00 00 30 '....Ü...0
RESPONSE: 000122: Bulk or Interrupt Transfer (UP), 03.09.2007 12:49:26.0 +0.0 Pipe Handle: 0x863ce214 (Endpoint Address: 0x81) Get 0xc bytes from the device: 0C 00 00 00 03 00 01 20 23 00 00 00 ....... #... Length TYPE CODE Trans#
One send (OUT to the device), two reads (IN from the device).
All three byte chunks commands are sent/recieved/recieeved by the function ptp_transaction() in the file ptp.c.
It boils down to ptp_usb_sendreq(), optionally ptp_usb_senddata() or ptp_usb_getdata() and finally ptp_usb_getresp() in the file libusb-glue.c. Notice ptp_usb_sendreq() and ptp_usb_getresp() are ALWAYS called. The TYPE field correspond to this, so the TYPES in this case are "COMMAND" (0x0001), "DATA" (0x0002), and "RESPONSE" (0x0003).
Notice that the byte order is little endian, so you need to read each field from right to left.
This COMMAND has: CMD 0x99805, we see in ptp.h that this is PTP_OC_MTP_GetObjPropList. Transaction# 0x00000023. REQUEST parameters 0x10000327, 0x00000000, 0x0000DC02, 0x00000000 0x00000000, in this case it means "get props for object 0x10000327", "any format", "property 0xDC02" (PTP_OPC_ObjectFormat), then two parameters that are always zero (no idea what they mean or their use).
The DATA has: CMD 0x99805, we see in ptp.h that this is PTP_OC_MTP_GetObjPropList. Transaction# 0x00000023. Then comes data 0x00000001, 0x10000327, 0xDC02, 0x0004, 0x3000 Which means in this case, (and this is the tricky part) "here you have 1 property", "for object 0x10000327", "it is property 0xDC02" (PTP_OPC_ObjectFormat), "which is of type 0x0004" (PTP_DTC_UINT16), "and set to 0x3000" (PTP_OFC_Undefined, it is perfectly valid to have undefined object formats, since it is a legal value defining this).
This RESPONSE has: CMD 0x99805, we see in ptp.h that this is PTP_OC_MTP_GetObjPropList. Return Code ("RC") = 0x2001, PTP_RC_OK, all went fine. Transaction# 0x00000023.
If you want to compare the Windows behaviour with a similar operation using libmtp you can go into the src/libusb-glue.c file and uncomment the row that reads:
//#define ENABLE_USB_BULK_DEBUG
(I.e. remove the two //.)
This will make libmtp print out a hex dump of every bulk USB transaction. The bulk transactions contain all the PTP/MTP layer data, which is usually where the problems appear.
In debugging new hardware, we highly recommend that you only use the example mtp-* applications that come with libmtp, as other applications may have their own bugs that may interfere with your new device working correctly. Using another application instead of those that come with libmtp just adds another point of failure.
For debugging, there are 3 main options:
(Assuming bash) eg: $ export LIBMTP_DEBUG=12 $ mtp-detect // To get USB debug and USB data debug information.
$ export LIBMTP_DEBUG=2 $ mtp-detect // To get Playlist debug information.
Also note, an application may also use the LIBMTP_debug() API function to achieve the same options as listed above.
This will at least help pinpoint where the application is failing, or a device is reporting incorrect information. (This is extremely helpful with devices that have odd disconnection requirements).
The use of these tools may also pinpoint issues with libusb as implemented by each OS vendor or issues with the MTP implementation on the new device as well, so please be prepared for either case.
The use of gdb or another debugger may also miss or actually cause command and data timing issues with some devices, leading to false information. So please consider this a last resort option.
Also please read the "It's Not Our Bug!" section below, as it does contain some useful information that may assist with your device.
Some devices that are dual-mode are simply impossible to get to work under Linux because the usb-storage(.ko) kernel module hook them first, and refuse to release them, even when we specify the DEVICE_FLAG_UNLOAD_DRIVER flag. (Maybe it DOES release it but the device will immediately be probed at the USB mass storage interface AGAIN because it enumerates.)
Here is what some people do:
Linux: Try this, if you have a recent 2.6.x Linux kernel, run (as root) something like:
rmmod usb_storage ; mtp-detect
You can run most any command or a client like gnomad2 or Amarok immediately after the rmmod command. This works sometimes. Another way:
Edit /etc/modprobe.d/blacklist
Add the line "blacklist usb-storage"
Reboot.
Now none of you USB disks, flash memory sticks etc will be working (you just disabled them all). However you can try your device, and it might have started working because there is no longer a USB mass storage driver that tries to hook onto the mass storage interface of your device.
If not even blacklisting works (check with
"lsmod | grep usb-storage"), there is some problem with
something else and you may need to remove or rename the file
/lib/modules/
If you find the PerfectSolution(TM) to this dilemma, so you can properly switch for individual devices whether to use it as USB mass storage or not, please tell us how you did it. We know we cannot use udev, because udev is called after-the-fact: the device is already configured for USB mass storage when udev is called.
On Mac OS there is another ugly hack:
and when prompted enter your password.
To reverse this change, just reverse the filenames:
sudo mv /System/Library/Extensions/ IOUSBMassStorageClass.kext.disabled /System/Library/Extensions/ IOUSBMassStorageClass.kext
and restart.
The Creative Zen series can read VCALENDAR2 (.ics) files and VCard (.vcf) files from programs like for example Evolution with the following limitations/conditions:
The file must be in DOS (CR/LF) format, use the unix2dos program to convert if needed
Repeat events in calendar files do not seem to be supported, entries will only appear once.
Calendar (.ics) files should be stored in the folder "My Organizer" when sent to the device (this directory should be autodetected for use with calendar files, otherwise use the option -f "My Organizer" to sendfile for this) Apparently this file can also contain tasklists.
Contact (.vcf) files should be stored in the folder "My Contacts" when sent to the device. (-f "My Contacts")
Some devices are picky about the name of the calendar and contact files. For example the Zen Microphoto wants:
Calendar: My Organizer/6651416.ics Contacts: My Organizer/6651416.vcf
Evolution can easily export .ics an .vcf files, but you currently need some command-line hacking to get you stuff copied over in one direction host -> device. The examples/ directory contains a script created for the Creative Zen Microphoto by Nicolas Tetreault.
Shared libraries can be troublesome to users not experienced with them. The following is a condensed version of a generic question that has appeared on the libmtp mailing list from time to time.
PTP: Opening session Queried Creative Zen Vision:M gnomad2: relocation error: gnomad2: undefined symbol: LIBMTP_Get_Storageinfo (...) Are these type of errors related to libmtp or something else?
The problem is of a generic nature, and related to dynamic library loading. It is colloquially known as "dependency hell". (http://en.wikipedia.org/wiki/Dependency_hell)
The gnomad2 application calls upon the dynamic linker in Linux to resolve the symbol "LIBMTP_Get_Storageinfo" or any other symbol (ELF symbol, or link point or whatever you want to call them, a symbol is a label on a memory address that the linker shall resolve from label to actual address.) For generic information on this subject see the INSTALL file and this Wikipedia page:
http://en.wikipedia.org/wiki/Library_(computing)
When Linux /lib/ld-linux.so.X is called to link the symbols compiled into gnomad2 (or any other executable using libmtp), it examines the ELF file for the libmtp.so.X file it finds first and cannot resolve the symbol "LIBMTP_Get_Storageinfo" (or whichever symbol you have a problem witj) from it, since it's probably not there. There are many possible causes of this symbol breakage:
1) You installed precompiled libmtp and gnomad2 packages (RPMs, debs whatever) that do not match up. Typical cause: your gnomad2 package was built against a newer version of libmtp than what's installed on your machine. Another typical cause: you installed a package you found on the web, somewhere, the dependency resolution system did not protest properly (as it should) or you forced it to install anyway, ignoring some warnings.
2) You compiled libmtp and/or gnomad2 from source, installing both or either in /usr/local/lib and /usr/local/bin. This means at compile-time gnomad2 finds the libmtp library in /usr/local/lib but at runtime, it depends on the Linux system wide library loader (/lib/ld-linux.so.X) in order to resolve the symbols. This loader will look into the file /etc/ld.so.conf and/or the folder /etc/ld.so.conf.d in order to find paths to libraries to be used for resolving the symbols. If you have some older version of libmtp in e.g. /usr/lib (typically installed by a package manager) it will take precedence over the new version you just installed in /usr/local/lib and the newly compiled library in /usr/local/lib will not be used, resulting in this error message.
3) You really did install the very latest versions (as of writing libmtp 0.1.5 and gnomad2 2.8.11) from source and there really is no pre-installed package of either on your machine. In that case I'm totally lost, I have no idea what's causing this.
Typical remedies:
1) If you don't want to mess around with your system and risk these situations, only use pre-packaged software that came with the distribution or its official support channels. If it still breaks, blame your distribution, they're not packaging correctly. Relying on properly packaged software and not installing things yourself is the Linux solution to the "dependency hell" problem.
2) Read about dynamically linked library handling until the stuff I wrote about in the previous list sounds like music to your ears, inspect your /lib, /usr/lib, /usr/local/lib, /etc/ld.so.conf and the /etc/ld.so.conf.d, remove all pre-packed versions using RPM, APT, YaST or whatever your distribution uses, compile libmtp and gnomad2 (or whatever) from source only and you will be enlighted.
I don't know if this helps you, it's the best answer we can give.
PTP/MTP devices does not actually contain "files", they contain objects. These objects have file names, but that is actually just a name tag on the object.
Folders/directories aren't really such entities: they are just objects too, albeit objects that can act as parent to other objects. They are called "associations" and are created in atomic fashion and even though there is an MTP command to get all the associations of a certain object, this command is optional so it is perfectly possible (and most common, actually) to create devices where the "folders" (which are actually associations) have no idea whatsoever of what files they are associated as parents to (i.e. which files they contain). This is very easy for device manufacturers to implement, all the association (i.e. finding out which files are in a certain folder) has to be done by the MTP Initiator / host computer.
Moving a file to a new folder is for example very simple in a "real" file system. In PTP/MTP devices it is often not even possible, some devices may be able to do that, if they support command 0x1019 "Move Object", but actually the only reliable way of executing file movement is to upload the file to the host, download it with the new parent, then delete the old file. We have played with the idea of implementing this time consuming function as a fallback in case the device does not support command 0x1019, perhaps one day we will do that. (Some devices also support command 0x101a "Copy Object".)
Then the issue that in PTP/MTP it is legal for two files to have exactly the same path as long as their object IDs differ. A folder/association can contain two files with the exact same name. (And on the Creative devices this even works, too, though most devices implicitly fail at this.) Perhaps one could add some custom hook for handling that, so they become /Foo.mp3 and /Foo.mp3(1) or something similar, but it's really a bit kludgy.
Playlists and albums aren't really files, thinking about them as files like the hacks in libgphoto2 is really backwards. They are called associations and are more like a symbolic link that links in a star-shaped pattern to all the files that are part of the album/playlist. Some devices (Samsung) thought that was too complicated and have a different way of storing playlists in an UTF-16 encoded .spl-like file instead! This is why playlists/albums must have their own structs and functions.
Plain file access also assumes to be able to write files of an undetermined size, which is simply not possible in a transactional file system like PTP/MTP. (See further below.)
Streaming reads is easy. Just connect the output file descriptor from LIBMTP_Get_File_To_File_Descriptor() (and a similar function for tracks) wherever you want.
People have connected this to TCP sockets for streaming web servers etc, works like a charm. Some devices will even survive if the callback functions return non-zero and cancel the download. Some devices will lock up and even require a reset if you do that. Devices are poorly implemented so that's life. If you want to stream off a device, the best idea is always to stream the entire file and discard the stuff at the end you don't want. It will incur a delay if you e.g. want to skip between tracks, sadly.
Then we get to the complicated things: streaming WRITES...
There is a function: LIBMTP_Send_File_From_File_Descriptor() (and similar for tracks) which will write a file to a device from a file descriptor, which may be a socket or whatever.
HOWEVER: this requires a piece of metadata with the .filesize properly set first.
This is not because we think it is funny to require that, the protocol requires it. The reason is that PTP/MTP is a transactional file system and it wants to be able to deny file transfer if the file won't fit on the device, so the transaction never even starts, it's impossible to start a transaction without giving file length.
People really want streaming so I tried a lot of hacks to see if they would work, such as setting file size to 0xffffffffU or something other unnaturally big and then aborting the file transfer when the stream ends. It doesn't work: either the device crashes or the file simply disappears since the device rolls back all failed transactions.
So this is an inherent limitation of the PTP/MTP protocol.
I have both good and bad news for you.
The good news is that the MTP protocol has well-defined commands to play back content on a device. Operation 0xD411 (PTP_DPC_MTP_PlaybackObject) will start playing back a file on the device (whatever that may mean if this is not a music or video file), and operation 0xD403 can set the playback volume to save your ears. Then there are operations to determine how far into the current file you currently are, so as to support say progress bars.
Since these commands have been around since the dawn of the MTP protocol and since it was developed in cooperation with Creative Technology, this is probably a requested feature from the Creative people who already had support for playback on their devices using the PDE protocol back then.
Anyway, here are the bad news: [logs]$ grep d411 * mtp-detect-trekstor-vibez.txt: 0xd411: Playback Object
Aha there is only one known device in the world which actually supports playback on the device. So either you go buy the Trekstor Vibez, or you can forget about this. You could always try asking your hardware vendor of choice to go implement this.
Since none of the core developers of libmtp has the Trekstor device, this is not yet implemented in libmtp.
If you are a device vendor there is a lot you can do for libmtp:
Please consider assigning one of your employees as a contact person for libmtp, have them sign up to the libmtp development list and answer questions and post new device ID:s as they are released to our mailing list.
If you want to help even more, assign someone to look deeper into error reports on your specific devices, understand why your firmware may require some special device flags and what can be done about it.
Do you have spare devices you can give us? Send them to Richard (Mac support) or Linus (Linux support). (So far nobody did that except for Microsoft who sent us a Zune by proxy!)
Vendors do need help from libmtp too, especially we want to help vendors improve their MTP stacks, because they all suffer from the same problem: the lack of a proper conformance test has made many devices incompliant with the MTP specification as it is published today: most devices are just compliant with the Windows MTP stack, and don't work out-of-the-box with libmtp. We need someone on the inside to help in bug reporting vendors MTP stacks internally so these issues are raised. A good way to go toward better MTP compliance is to test with an alternative implementation of the stack. In e.g. IETF standardization it is compulsory for an RFC to have atleast two independent implementations for it to reach the status as standard.
Being compliant with libmtp is also more and more important for vendors: libmtp is being deployed in some embedded systems like set-top-boxes etc. It will be very irritating for customers if a device will not dock properly with some home entertainment equipment just because it is based on Linux and libmtp and not the Windows MTP stack.
Previously you would use HAL to detect devices being plugged in. Nowadays we use udev directly, or though the GNOME libgudev library. LIBMTPs default udev rules export the proper properties to detect any MTP device automatically, here is a verbose example derived from gnomad2:
const char const gudev_subsystems[] = { "usb", NULL }; GUdevClient gudev_client; guint uevent_id; guint uevent_bus_hooked = 0; guint uevent_device_hooked = 0;
static void uevent_cb(GUdevClient client, const char action, GUdevDevice device, void data) { guint64 devicenum; guint vendor; guint model; guint busnum; guint devnum; guint mtpdevice;
devicenum = (guint64) g_udev_device_get_device_number(device); g_print("%s event for %s (%"G_GINT64_MODIFIER"x)", action, g_udev_device_get_sysfs_path (device), devicenum);
/ get device info / vendor = get_property_as_int(device, "ID_VENDOR_ID", 16); model = get_property_as_int(device, "ID_MODEL_ID", 16); busnum = get_property_as_int(device, "BUSNUM", 10); devnum = get_property_as_int(device, "DEVNUM", 10); mtpdevice = get_property_as_int(device, "ID_MTP_DEVICE", 10);
if (vendor == 0 || model == 0) { g_print("couldn't get vendor or model ID for device at (%x:%x)\n", busnum, devnum); return; } else { g_print("vendor = %x, model = %x, bus = %x, device = %x\n", vendor, model, busnum, devnum); }
if (mtpdevice) { g_print("device is MTP compliant\n");
if (g_str_equal(action, "add") &&
uevent_bus_hooked == 0 &&
uevent_device_hooked == 0) {
g_print(MTP device plugged in!\n");
uevent_bus_hooked = busnum;
uevent_device_hooked = devnum;
scan_jukebox(NULL);
} else if (g_str_equal (action, "remove") &&
uevent_bus_hooked == busnum &&
uevent_device_hooked == devnum) {
g_print("MTP device removed!\n");
uevent_bus_hooked = 0;
uevent_device_hooked = 0;
}} }
(...) /*
Draft agenda for a talk on MTP devices submitted for the Android builders summit, might come to recycle this: