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Date: Tue, 21 May 2019 15:05:31 +0000 From: David Laight <David.Laight@...LAB.COM> To: 'Chang-Hsien Tsai' <luke.tw@...il.com>, "netdev@...r.kernel.org" <netdev@...r.kernel.org> CC: "ast@...nel.org" <ast@...nel.org>, "daniel@...earbox.net" <daniel@...earbox.net>, "kafai@...com" <kafai@...com>, "songliubraving@...com" <songliubraving@...com>, "yhs@...com" <yhs@...com> Subject: RE: [PATCH] samples: bpf: fix: change the buffer size for read() From: Chang-Hsien Tsai > Sent: 19 May 2019 10:06 > If the trace for read is larger than 4096, > the return value sz will be 4096. > This results in off-by-one error on buf. > > static char buf[4096]; > ssize_t sz; > > sz = read(trace_fd, buf, sizeof(buf)); > if (sz > 0) { > buf[sz] = 0; > puts(buf); > } > > Signed-off-by: Chang-Hsien Tsai <luke.tw@...il.com> > --- > samples/bpf/bpf_load.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/samples/bpf/bpf_load.c b/samples/bpf/bpf_load.c > index eae7b635343d..d4da90070b58 100644 > --- a/samples/bpf/bpf_load.c > +++ b/samples/bpf/bpf_load.c > @@ -678,7 +678,7 @@ void read_trace_pipe(void) > static char buf[4096]; > ssize_t sz; > > - sz = read(trace_fd, buf, sizeof(buf)); > + sz = read(trace_fd, buf, sizeof(buf)-1); > if (sz > 0) { > buf[sz] = 0; > puts(buf); Why not change the puts() to fwrite(buf, sz, 1, stdout) ? Then you don't need the '\0' terminator. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
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