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OK, the USB gadget serial driver actually has a couple of problems. On gs_open(), it always allocates and queues an additional QUEUE_SIZE (16) worth of requests, so with a loop like this: i=1 ; while echo $i > /dev/ttyGS0 ; do let i++ ; done eventually we run into OOM (Out of Memory). Technically, it is not a leak as everything gets freed up when the USB connection is broken, but not on gs_close(). With a USB device/gadget controller driver that has limited resources (e.g., Marvell has a this MAX_XDS_FOR_TR_CALLS of 64 for transmit and receive), so even after 4 stty -F /dev/ttyGS0 we cannot transmit anymore. We can still receive (not necessarily reliably) as now we have 16 * 4 = 64 descriptors/buffers ready, but the device is otherwise not usable. Signed-off-by: Jim Sung <jsung@syncadence.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
To understand all the Linux-USB framework, you'll use these resources: * This source code. This is necessarily an evolving work, and includes kerneldoc that should help you get a current overview. ("make pdfdocs", and then look at "usb.pdf" for host side and "gadget.pdf" for peripheral side.) Also, Documentation/usb has more information. * The USB 2.0 specification (from www.usb.org), with supplements such as those for USB OTG and the various device classes. The USB specification has a good overview chapter, and USB peripherals conform to the widely known "Chapter 9". * Chip specifications for USB controllers. Examples include host controllers (on PCs, servers, and more); peripheral controllers (in devices with Linux firmware, like printers or cell phones); and hard-wired peripherals like Ethernet adapters. * Specifications for other protocols implemented by USB peripheral functions. Some are vendor-specific; others are vendor-neutral but just standardized outside of the www.usb.org team. Here is a list of what each subdirectory here is, and what is contained in them. core/ - This is for the core USB host code, including the usbfs files and the hub class driver ("khubd"). host/ - This is for USB host controller drivers. This includes UHCI, OHCI, EHCI, and others that might be used with more specialized "embedded" systems. gadget/ - This is for USB peripheral controller drivers and the various gadget drivers which talk to them. Individual USB driver directories. A new driver should be added to the first subdirectory in the list below that it fits into. image/ - This is for still image drivers, like scanners or digital cameras. ../input/ - This is for any driver that uses the input subsystem, like keyboard, mice, touchscreens, tablets, etc. ../media/ - This is for multimedia drivers, like video cameras, radios, and any other drivers that talk to the v4l subsystem. ../net/ - This is for network drivers. serial/ - This is for USB to serial drivers. storage/ - This is for USB mass-storage drivers. class/ - This is for all USB device drivers that do not fit into any of the above categories, and work for a range of USB Class specified devices. misc/ - This is for all USB device drivers that do not fit into any of the above categories.