net: recv(): return -EAGAIN instead of 0 when no cleanup is expected
Some drivers do not behave properly when free_pkt() is called with a
length of zero. It is an issue I observed when developing the lwIP
series [1] (see "QEMU CI tests for r2dplus_i82557c, r2dplus_rtl8139"
in the change log) and which I fixed incorrectly by not calling
free_pkt() when recv() returns 0. That turned out to be wrong for two
reasons:
1. The DM documentation [2] clearly requires it:
"The **recv** function polls for availability of a new packet. [...]
If there is an error [...], return 0 if you require the packet to
be cleaned up normally, or a negative error code otherwise (cleanup
not necessary or already done).
If **free_pkt** is defined, U-Boot will call it after a received
packet has been processed [...]. free_pkt() will be called after
recv(), for the same packet [...]"
2. The imx8mp_evk platform will fail with OOM errors if free_pkt() is
not called after recv() returns 0:
u-boot=> tftp 192.168.0.16:50M
Using ethernet@30be0000 device
TFTP from server 192.168.0.16; our IP address is 192.168.0.48
Filename '50M'.
Load address: 0x40480000
Loading: #######################fecmxc_recv: error allocating packetp
fecmxc_recv: error allocating packetp
fecmxc_recv: error allocating packetp
...
Therefore, make recv() return -EAGAIN instead of 0 when no packet is
available and the driver doesn't expect free_pkt() to be called
subsequently.
[1] https://lists.denx.de/pipermail/u-boot/2024-August/562861.html
[2] doc/develop/driver-model/ethernet.rst
Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
2 files changed