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Modify libusb to accept file descriptor

I changed the libusb1.0 open function as follows:

static int op_open2(struct libusb_device_handle *handle, int fd) { struct linux_device_handle_priv *hpriv = _device_handle_priv(handle); hpriv->fd = fd; return usbi_add_pollfd(HANDLE_CTX(handle), hpriv->fd, POLLOUT); }

where fd was obtained through android.hardware.usb.UsbDeviceConnection.html # getFileDescriptor ()

 final UsbDeviceConnection connection = manager.openDevice(device); return connection.getFileDescriptor();

Unfortunately, I always get an error message when calling

 static int op_claim_interface(struct libusb_device_handle *handle, int iface) { int fd = _device_handle_priv(handle)->fd; int r = ioctl(fd, IOCTL_USBFS_CLAIMINTF, &iface); if (r) { if (errno == ENOENT) return LIBUSB_ERROR_NOT_FOUND; else if (errno == EBUSY) return LIBUSB_ERROR_BUSY; else if (errno == ENODEV) return LIBUSB_ERROR_NO_DEVICE; usbi_err(HANDLE_CTX(handle), "claim interface failed, error %d errno %d", r, errno); return LIBUSB_ERROR_OTHER; } return 0; }

request interface failed, error -1 errno 9

which translates to Bad File Number. The file descriptor I get from Java is a positive integer!

The only small detail is that my own code works as a separate binary file that is created using Java ProcessBuilder. But they have the same uid, so I assume that the USB permissions that I have in Java should still apply to libusb.

I don’t need to be platform independent, so any hacks would do the job :)

Any thoughts would be greatly appreciated!

Additional Information! The output I get from lsof (shortened to emphasize its most interesting part)

 my.activity 13374 u0_a62 exe ??? ??? ??? ??? /system/bin/app_process my.activity 13374 u0_a62 0 ??? ??? ??? ??? /dev/null my.activity 13374 u0_a62 1 ??? ??? ??? ??? /dev/null my.activity 13374 u0_a62 2 ??? ??? ??? ??? /dev/null my.activity 13374 u0_a62 3 ??? ??? ??? ??? /dev/log/main my.activity 13374 u0_a62 4 ??? ??? ??? ??? /dev/log/radio my.activity 13374 u0_a62 5 ??? ??? ??? ??? /dev/log/events my.activity 13374 u0_a62 6 ??? ??? ??? ??? /dev/log/system my.activity 13374 u0_a62 7 ??? ??? ??? ??? /system/framework/core.jar my.activity 13374 u0_a62 8 ??? ??? ??? ??? /system/framework/core-junit.jar my.activity 13374 u0_a62 9 ??? ??? ??? ??? /dev/__properties__ (deleted) ... my.activity 13374 u0_a62 44 ??? ??? ??? ??? /dev/bus/usb/002/002 ... my.activity 13374 u0_a62 51 ??? ??? ??? ??? pipe:[51015] my.activity 13374 u0_a62 53 ??? ??? ??? ??? pipe:[51016] ... my_exe 13546 u0_a62 exe ??? ??? ??? ??? /data/data/my.activity/files/my_exe my_exe 13546 u0_a62 0 ??? ??? ??? ??? pipe:[51015] my_exe 13546 u0_a62 1 ??? ??? ??? ??? pipe:[51016] my_exe 13546 u0_a62 2 ??? ??? ??? ??? pipe:[51016] my_exe 13546 u0_a62 3 ??? ??? ??? ??? /dev/log/main my_exe 13546 u0_a62 4 ??? ??? ??? ??? /dev/log/radio my_exe 13546 u0_a62 5 ??? ??? ??? ??? /dev/log/events my_exe 13546 u0_a62 6 ??? ??? ??? ??? /dev/log/system my_exe 13546 u0_a62 9 ??? ??? ??? ??? /dev/__properties__ (deleted) my_exe 13546 u0_a62 mem ??? b3:09 0 302530 /data/data/my.activity/files/my_exe my_exe 13546 u0_a62 mem ??? b3:09 36864 302530 /data/data/my.activity/files/my_exe my_exe 13546 u0_a62 mem ??? b3:09 40960 302530 /data/data/my.activity/files/my_exe my_exe 13546 u0_a62 mem ??? b3:03 0 200 /system/bin/linker my_exe 13546 u0_a62 mem ??? b3:03 57344 200 /system/bin/linker my_exe 13546 u0_a62 mem ??? b3:03 61440 200 /system/bin/linker

Which makes me think that the file descriptor 44 that I pass to my_exe is not really inherited!

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2 answers

It turned out that the file descriptor was not inherited by the process. If you use JNI, everything should be fine, but if you want to interact with a third-party application, you will need to pass the file descriptor to the third-party application.

My solution was to use UNIX sockets to pass fd through JNI and it worked!

PS

I released the project under the GNU license - https://github.com/martinmarinov/rtl_tcp_andro-

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File descriptors are private to the process. Transferring them to another process as is is guaranteed that it will not work with any * nix flavor.

The Android Binder / Parcel IPC interface can create file descriptors.

Or you can inherit a descriptor - if it is already open, when the process is spawned, the descriptor will be valid in the spawned process.

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