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Add a note about the pager to the console documentation, with some more information in the developer section. Also include the pager API. Series-to: concept Cover-letter: Introduce a pager for the console Some U-Boot commands can produce a lot of output and this can run off top of the display. This series introduces a simple pager feature, to allow the output to be read, before pressing SPACE to continue. A fixed buffer size (4K) is used, which sets a limit on the permmited output before paging fails and the output is simply written all in one lot. In most cases this is plenty, but 'env print' does print the whole environment as one string, so if the legacy distro-boot scripts are used it could happen. The default number of visible lines is set with a Kconfig option. Where a video terminal is being used, the page size is set to match that. In general U-Boot cannot guess the number of visible lines, since a serial terminal may be in use. There is also a 'pager' environment variable which can override any detected value. This initial series only counts newlines. It has no support for counting characters so the result will be sub-optimal if very long lines are written. This could be addressed in a future patch. Some effort is made to handle common cases correctly. For example, if stdout is changed to a serial or vidconsole device, that is used to determine the page length. When redirecting sandbox to a file, no attempt is made. Future work may detect the terminal size by sending an ANSI sequence. END Signed-off-by: Simon Glass <sjg@chromium.org> Series-version: 2
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42 lines
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.. SPDX-License-Identifier: GPL-2.0+
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.. sectionauthor:: Simon Glass <sjg@chromium.org>
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=======
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Console
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=======
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Paging
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------
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See the user documentation at :doc:`/usage/console`. For the API, see
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:doc:`/api/pager`.
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The pager is implemented in `common/pager.c` and integrated into the console
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system via `console_puts()` in `common/console.c`. When output is sent to
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stdout:
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1. Text is passed to `pager_post()` which buffers it
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2. `pager_next()` returns portions of text up to the page limit
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3. When the page limit is reached, a prompt is displayed
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4. The system waits for user input (SPACE key) via `getchar()`
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5. After SPACE is pressed, the prompt is cleared and output continues
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The pager maintains state through the `struct pager` which tracks:
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- Current line count within the page
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- Page length setting
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- Text buffer and overflow handling
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- Current pager state (normal, waiting for user, clearing prompt)
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Bypass Mode
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~~~~~~~~~~~
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The pager can be put into bypass mode using `pager_set_bypass()`, which is
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useful for automated testing. In bypass mode, all text flows through without
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any paging interruptions.
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The pager automatically enters bypass mode when output is not connected to a
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terminal, preventing paging prompts from appearing in non-interactive
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environments like scripts or automated builds.
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