net: Accept4 issues with old Linux 2.6 kernels

[gopherbot]

by todd.richmond:

Go 1.1 and 1.2 both fail to listen on old, early rev Linux kernels such as those found
on QNAP NAS boxes running any modern version of their firmware

Accept4 is not available on those systems, but for some reason arm
and amd64 kernels are returning different errors so checks for both EACCES and EFAULT are
both required. A Go web server will fallback correctly to the accept() call with this
check

Line 48 of src/pkg/net/sock_cloexec.go

if err == nil || (err != syscall.EACCES && err != syscall.EFAULT && err
!=
syscall.ENOSYS && err != syscall.EINVAL) {

[davecheney]

Comment 1:

How old are we talking here ?

[gopherbot]

Comment 2 by todd.richmond:

QNAP kernels from the currently shipping firmwares are 2.6.33.2 - something like 7 years
out of date! It looks like the firmware they have just started shipping (manual
downloads only, not automatic) are 3.x and will work fine. However, I'm not sure they
will update all their previous hardware systems because many of those have less internal
memory
This fix is safe regardless because if something was wrong, it would be caught again in
the fallback accept() call

[davecheney]

Comment 3:

That should be ok. Going much earlier would lead to problems with sync/atomic as they
were broken before 2.6.29 and really broken before 2.6.27

Labels changed: added release-go1.3, repo-main, arch-arm.

Status changed to Started.

[rsc]

Comment 4:

https://golang.org/cl/84170043

[gopherbot]

Comment 5 by todd.richmond:

that switch statement will also work - just a bit harder to follow as it's more
customary to use multiple cases with a final break instead of default being first and
having the remaining fall off the bottom. Does save 1 line of text though ;) - and
executes the same

[rsc]

Comment 6:

This issue was closed by revision 5fb39cc.

Status changed to Fixed.