From 40cdf69fc9279ab28f84a6e0f965de8382c578fe Mon Sep 17 00:00:00 2001 From: Andy Pan Date: Tue, 17 Oct 2023 22:38:17 +0800 Subject: [PATCH] internal/poll: add SPLICE_F_NONBLOCK flag for splice to avoid inconsistency with O_NONBLOCK For #59041 Details: https://github.com/golang/go/issues/59041#issuecomment-1766610087 Change-Id: Id3fc1df6d86b7c4cc383d09f9465fa8f4cc2a559 Reviewed-on: https://go-review.googlesource.com/c/go/+/536015 Reviewed-by: Bryan Mills Reviewed-by: Ian Lance Taylor LUCI-TryBot-Result: Go LUCI Auto-Submit: Ian Lance Taylor --- src/internal/poll/splice_linux.go | 21 +++++++++++++++++++-- 1 file changed, 19 insertions(+), 2 deletions(-) diff --git a/src/internal/poll/splice_linux.go b/src/internal/poll/splice_linux.go index 9505c5dcfc1eb..72cca34fe4ae5 100644 --- a/src/internal/poll/splice_linux.go +++ b/src/internal/poll/splice_linux.go @@ -13,6 +13,12 @@ import ( ) const ( + // spliceNonblock doesn't make the splice itself necessarily nonblocking + // (because the actual file descriptors that are spliced from/to may block + // unless they have the O_NONBLOCK flag set), but it makes the splice pipe + // operations nonblocking. + spliceNonblock = 0x2 + // maxSpliceSize is the maximum amount of data Splice asks // the kernel to move in a single call to splice(2). // We use 1MB as Splice writes data through a pipe, and 1MB is the default maximum pipe buffer size, @@ -89,7 +95,11 @@ func spliceDrain(pipefd int, sock *FD, max int) (int, error) { return 0, err } for { - n, err := splice(pipefd, sock.Sysfd, max, 0) + // In theory calling splice(2) with SPLICE_F_NONBLOCK could end up an infinite loop here, + // because it could return EAGAIN ceaselessly when the write end of the pipe is full, + // but this shouldn't be a concern here, since the pipe buffer must be sufficient for + // this data transmission on the basis of the workflow in Splice. + n, err := splice(pipefd, sock.Sysfd, max, spliceNonblock) if err == syscall.EINTR { continue } @@ -127,7 +137,14 @@ func splicePump(sock *FD, pipefd int, inPipe int) (int, error) { } written := 0 for inPipe > 0 { - n, err := splice(sock.Sysfd, pipefd, inPipe, 0) + // In theory calling splice(2) with SPLICE_F_NONBLOCK could end up an infinite loop here, + // because it could return EAGAIN ceaselessly when the read end of the pipe is empty, + // but this shouldn't be a concern here, since the pipe buffer must contain inPipe size of + // data on the basis of the workflow in Splice. + n, err := splice(sock.Sysfd, pipefd, inPipe, spliceNonblock) + if err == syscall.EINTR { + continue + } // Here, the condition n == 0 && err == nil should never be // observed, since Splice controls the write side of the pipe. if n > 0 {