Rich Felker
e7eeeb9f2a
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.
25 lines
611 B
C
25 lines
611 B
C
#include "stdio_impl.h"
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#include <sys/uio.h>
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size_t __stdio_read(FILE *f, unsigned char *buf, size_t len)
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{
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struct iovec iov[2] = {
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{ .iov_base = buf, .iov_len = len - !!f->buf_size },
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{ .iov_base = f->buf, .iov_len = f->buf_size }
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};
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ssize_t cnt;
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cnt = iov[0].iov_len ? syscall(SYS_readv, f->fd, iov, 2)
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: syscall(SYS_read, f->fd, iov[1].iov_base, iov[1].iov_len);
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if (cnt <= 0) {
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f->flags |= cnt ? F_ERR : F_EOF;
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return 0;
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}
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if (cnt <= iov[0].iov_len) return cnt;
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cnt -= iov[0].iov_len;
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f->rpos = f->buf;
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f->rend = f->buf + cnt;
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if (f->buf_size) buf[len-1] = *f->rpos++;
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return len;
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}
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