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Kernel: Fix assertion failure on large TTY writes

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The `File::can_write` mechanism lets us check that writes won't block,
meaning some bytes can be immediately written to the underlying device.
This means calling `File::write` in a situation where no data could be
written is a logic error, which we `VERIFY()` in `Process::do_write()`.

TTY, in particular, processes the write in 256-byte buffered chunks.
Previously, we would assert that none of these sub-writes returned zero.
This was a logic error, as this rejected some successful writes. For
example, if there was exactly enough free space in `SlavePty`'s internal
buffer for the previous sub-write to complete fully. This made it
impossible to perform writes larger than `SlavePty`'s internal buffer.

Note that it's not an issue if `on_tty_write` returns zero, as partial
writes are handled correctly by the `buffer.read_buffered` helper. We
won't spin in a loop trying to write to a full buffer.

Fixes #8090
This commit is contained in:
Daniel Bertalan 2021-06-21 15:49:34 +02:00 • committed by Andreas Kling
parent 08e2dc22be
commit ae6367999f
1 changed files with 0 additions and 1 deletions
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Kernel/TTY/TTY.cpp
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@ -97,7 +97,6 @@ KResultOr<size_t> TTY::write(FileDescription&, u64, const UserOrKernelBuffer& bu
});
}
auto bytes_written_or_error = on_tty_write(UserOrKernelBuffer::for_kernel_buffer(modified_data), modified_data_size);
VERIFY(bytes_written_or_error.is_error() || bytes_written_or_error.value() != 0);
if (bytes_written_or_error.is_error() || !(m_termios.c_oflag & OPOST) || !(m_termios.c_oflag & ONLCR))
return bytes_written_or_error;
auto bytes_written = bytes_written_or_error.value();