From e7eeeb9f2a4a358fb0bbed81e145ef5538ff60f0 Mon Sep 17 00:00:00 2001
From: Rich Felker <dalias@aerifal.cx>
Date: Sat, 24 Feb 2018 11:19:54 -0500
Subject: 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(-)
(limited to 'src')
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;
--
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