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internal/poll: disable splice on old linux versions

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The splice syscall is buggy prior to linux 2.6.29. Instead of returning
0 when reading a closed socket, it returns EAGAIN.  While it is possible
to detect this (HAProxy falls back to recv), it is simpiler to avoid
using splice all together. the "fcntl(fd, F_GETPIPE_SZ)" syscall is used
detect buggy versions of splice as the syscall returns EINVAL on
versions prior to 2.6.35.

Fixes #25486

Change-Id: I860c029f13de2b09e95a7ba39b76ac7fca91a195
Reviewed-on: https://go-review.googlesource.com/113999
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Ben Burkert 2018-05-21 19:28:19 -07:00 committed by Brad Fitzpatrick
parent 132900982c
commit 92bdfab795
1 changed files with 28 additions and 29 deletions
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57
src/internal/poll/splice_linux.go
View File

@ -4,7 +4,11 @@
package poll
import "syscall"
import (
"sync/atomic"
"syscall"
"unsafe"
)
const (
// spliceNonblock makes calls to splice(2) non-blocking.
@ -134,43 +138,38 @@ func splice(out int, in int, max int, flags int) (int, error) {
return int(n), err
}
var disableSplice unsafe.Pointer
// newTempPipe sets up a temporary pipe for a splice operation.
func newTempPipe() (prfd, pwfd int, sc string, err error) {
p := (*bool)(atomic.LoadPointer(&disableSplice))
if p != nil && *p {
return -1, -1, "splice", syscall.EINVAL
}
var fds [2]int
// pipe2 was added in 2.6.27 and our minimum requirement is 2.6.23, so it
// might not be implemented. Falling back to pipe is possible, but prior to
// 2.6.29 splice returns -EAGAIN instead of 0 when the connection is
// closed.
const flags = syscall.O_CLOEXEC | syscall.O_NONBLOCK
if err := syscall.Pipe2(fds[:], flags); err != nil {
// pipe2 was added in 2.6.27 and our minimum requirement
// is 2.6.23, so it might not be implemented.
if err == syscall.ENOSYS {
return newTempPipeFallback(fds[:])
}
return -1, -1, "pipe2", err
}
return fds[0], fds[1], "", nil
}
// newTempPipeFallback is a fallback for newTempPipe, for systems
// which do not support pipe2.
func newTempPipeFallback(fds []int) (prfd, pwfd int, sc string, err error) {
syscall.ForkLock.RLock()
defer syscall.ForkLock.RUnlock()
if err := syscall.Pipe(fds); err != nil {
return -1, -1, "pipe", err
if p == nil {
p = new(bool)
defer atomic.StorePointer(&disableSplice, unsafe.Pointer(p))
// F_GETPIPE_SZ was added in 2.6.35, which does not have the -EAGAIN bug.
if _, _, errno := syscall.Syscall(syscall.SYS_FCNTL, uintptr(fds[0]), syscall.F_GETPIPE_SZ, 0); errno != 0 {
*p = true
destroyTempPipe(fds[0], fds[1])
return -1, -1, "fcntl", errno
}
}
prfd, pwfd = fds[0], fds[1]
syscall.CloseOnExec(prfd)
syscall.CloseOnExec(pwfd)
if err := syscall.SetNonblock(prfd, true); err != nil {
CloseFunc(prfd)
CloseFunc(pwfd)
return -1, -1, "setnonblock", err
}
if err := syscall.SetNonblock(pwfd, true); err != nil {
CloseFunc(prfd)
CloseFunc(pwfd)
return -1, -1, "setnonblock", err
}
return prfd, pwfd, "", nil
return fds[0], fds[1], "", nil
}
// destroyTempPipe destroys a temporary pipe.