From e7eeeb9f2a4a358fb0bbed81e145ef5538ff60f0 Mon Sep 17 00:00:00 2001 From: Rich Felker Date: Sat, 24 Feb 2018 11:19:54 -0500 Subject: [PATCH] avoid use of readv syscall in __stdio_read backend when not needed formally, calling readv with a zero-length first iov component should behave identically to calling read on just the second component, but presence of a zero-length iov component has triggered bugs in some kernels and performs significantly worse than a simple read on some file types. --- src/stdio/__stdio_read.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/src/stdio/__stdio_read.c b/src/stdio/__stdio_read.c index 909c36a9..ea675da3 100644 --- a/src/stdio/__stdio_read.c +++ b/src/stdio/__stdio_read.c @@ -9,7 +9,8 @@ size_t __stdio_read(FILE *f, unsigned char *buf, size_t len) }; ssize_t cnt; - cnt = syscall(SYS_readv, f->fd, iov, 2); + cnt = iov[0].iov_len ? syscall(SYS_readv, f->fd, iov, 2) + : syscall(SYS_read, f->fd, iov[1].iov_base, iov[1].iov_len); if (cnt <= 0) { f->flags |= cnt ? F_ERR : F_EOF; return 0; -- 2.25.1