pkt-line: eliminate the need for static buffer in packet_write_gently()
Teach `packet_write_gently()` to write the pkt-line header and the actual buffer in 2 separate calls to `write_in_full()` and avoid the need for a static buffer, thread-safe scratch space, or an excessively large stack buffer. Change `write_packetized_from_fd()` to allocate a temporary buffer rather than using a static buffer to avoid similar issues here. These changes are intended to make it easier to use pkt-line routines in a multi-threaded context with multiple concurrent writers writing to different streams. Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Jeff Hostetler committed
Mar 15, 2021 at 21:08 UTC
7455e05e4e750451eb3c33359a2bc9050156750c
1 file changed
+20
-8
pkt-line.c
+20
-8
@@ -196,17 +196,26 @@ int packet_write_fmt_gently(int fd, const char *fmt, ...)
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static int packet_write_gently(const int fd_out, const char *buf, size_t size)
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{
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- static char packet_write_buffer[LARGE_PACKET_MAX];
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+ char header[4];
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size_t packet_size;
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- if (size > sizeof(packet_write_buffer) - 4)
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+ if (size > LARGE_PACKET_DATA_MAX)
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return error(_("packet write failed - data exceeds max packet size"));
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packet_trace(buf, size, 1);
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packet_size = size + 4;
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- set_packet_header(packet_write_buffer, packet_size);
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- memcpy(packet_write_buffer + 4, buf, size);
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- if (write_in_full(fd_out, packet_write_buffer, packet_size) < 0)
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+
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+ set_packet_header(header, packet_size);
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+
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+ /*
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+ * Write the header and the buffer in 2 parts so that we do
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+ * not need to allocate a buffer or rely on a static buffer.
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+ * This also avoids putting a large buffer on the stack which
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+ * might have multi-threading issues.
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+ */
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+
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+ if (write_in_full(fd_out, header, 4) < 0 ||
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+ write_in_full(fd_out, buf, size) < 0)
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return error(_("packet write failed"));
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return 0;
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}
@@ -244,20 +253,23 @@ void packet_buf_write_len(struct strbuf *buf, const char *data, size_t len)
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int write_packetized_from_fd(int fd_in, int fd_out)
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{
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- static char buf[LARGE_PACKET_DATA_MAX];
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+ char *buf = xmalloc(LARGE_PACKET_DATA_MAX);
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int err = 0;
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ssize_t bytes_to_write;
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while (!err) {
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- bytes_to_write = xread(fd_in, buf, sizeof(buf));
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- if (bytes_to_write < 0)
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+ bytes_to_write = xread(fd_in, buf, LARGE_PACKET_DATA_MAX);
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+ if (bytes_to_write < 0) {
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+ free(buf);
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return COPY_READ_ERROR;
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+ }
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if (bytes_to_write == 0)
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break;
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err = packet_write_gently(fd_out, buf, bytes_to_write);
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}
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if (!err)
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err = packet_flush_gently(fd_out);
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+ free(buf);
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return err;
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}
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