2.7. TFTP filesystem

barebox has read/write support for the Trivial File Transfer Protocol (TFTP, RFC1350).

TFTP is not designed as a filesystem. It does not have support for listing directories. This means a ls to a TFTP-mounted path will show an empty directory. Nevertheless, the files are there.

Example:

barebox:/ mount -t tftp 192.168.23.4 /mnt/tftp

In addition to the TFTP filesystem implementation, barebox does also have a tftp command.

2.7.1. RFC 7440 “windowsize” support

barebox supports the tftp windowsize option for downloading files. It is not implemented for uploads.

Generally, this option greatly improves the download speed (factors 4-30 are not uncommon). But choosing a too large windowsize can have the opposite effect. Performance depends on:

  • the network infrastructure: when the tftp server sends files with 1Gb/s but there are components in the network (switches or the target nic) which support only 100 Mb/s, packets will be dropped.

    The lower the internal buffers of the bottleneck components, the lower the optimal window size.

    In practice (iMX8MP on a Netgear GS108Ev3 with a port configured to 100 Mb/s) it had to be reduced to

    global tftp.windowsize=26

    for example.

  • the target network driver: datagrams from server will arive faster than they can be processed and must be buffered internally. For example, the fec-imx driver reserves place for

    #define FEC_RBD_NUM                64

    packets before they are dropped

  • partially the workload: copying downloaded files to ram will be faster than burning them into flash. Latter can consume internal buffers quicker so that windowsize might be reduced