Greetings! While using a usb-serial device as console, I've noticed some significant gaps in the kernel logs it receives. The problem can be reproduced in qemu like this (the kernel is a x86_64_defconfig with usb-serial enabled and with the ftdi_sio driver enabled): qemu-system-x86_64 -m 4G -kernel arch/x86_64/boot/bzImage -usb -device usb-serial,chardev=ser -chardev pty,id=ser -append 'console=ttyUSB0' (this will create a `pts` device that will connect to the other end of the emulated usb-serial) Then the logs look something like this: [ 1.006459] SELinux: Initializing. [ 1.011620] Mount-cache hash table entries: 8192 (order: 4, 65536 bytes, li[ 2.315341] ACPI: \_SB_.LNKD: Enabled at IRQ 11 This probably happens because of the code in `usb_serial_generic_write` which tries to insert the data into the fifo: count = kfifo_in_locked(&port->write_fifo, buf, count, &port->lock); Because added indications for when the result is less than expected and it showed significant losses. The return value is silently ignored in `usb_console_write` Also making the fifo bigger in `setup_port_bulk_out` helped (I made it 10 times bigger and there were no losses) The reason so much data is written at a short time is because usb-serial is initialized rather late, and when it is registered as a console, all the logs until this point are written to it. I'm not sure what the solution should be. Maybe we need to check whether the write in `console_emit_next_record` was successful and not increase the seq counter in this case. Any suggestions?
