Vincent JardinandTom Rini
c23eeeadfc
Document the dispatch path added by the former commit
fs: dispatch null_dev_desc_ok filesystems before lookup
Add a null-block-device interfaces section that:
* lists the three fstypes that can benefit of it (semihosting, ubifs,
sandbox) and the CONFIG option that builds each
* explains the '-' convention for the unused <dev[:part]> field
Suggested-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Vincent Jardin <vjardin@free.fr>
Reviewed-by: Simon Glass <sjg@chromium.org>
111 lines
2.8 KiB
ReStructuredText
111 lines
2.8 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0+:
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.. index::
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single: load (command)
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load command
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============
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Synopsis
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--------
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::
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load <interface> [<dev[:part]> [<addr> [<filename> [bytes [pos]]]]]
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Description
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-----------
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The load command is used to read a file from a filesystem into memory.
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The number of transferred bytes is saved in the environment variable filesize.
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The load address is saved in the environment variable fileaddr.
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interface
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interface for accessing the block device (mmc, sata, scsi, usb, ....)
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dev
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device number
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part
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partition number, defaults to 0 (whole device)
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addr
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load address, defaults to environment variable loadaddr or if loadaddr is
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not set to configuration variable CONFIG_SYS_LOAD_ADDR
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filename
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path to file, defaults to environment variable bootfile
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bytes
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maximum number of bytes to load
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pos
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number of bytes to skip
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part, addr, bytes, pos are hexadecimal numbers.
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Example
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-------
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::
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=> load mmc 0:1 ${kernel_addr_r} snp.efi
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149280 bytes read in 11 ms (12.9 MiB/s)
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=>
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=> load mmc 0:1 ${kernel_addr_r} snp.efi 1000000
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149280 bytes read in 9 ms (15.8 MiB/s)
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=>
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=> load mmc 0:1 ${kernel_addr_r} snp.efi 1000000 100
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149024 bytes read in 10 ms (14.2 MiB/s)
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=>
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=> load mmc 0:1 ${kernel_addr_r} snp.efi 10
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16 bytes read in 1 ms (15.6 KiB/s)
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=>
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Null-block-device interfaces
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----------------------------
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A few ``<interface>`` values have no underlying block device. Their
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filesystem implementations directly call a back-end (JTAG
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debugger, UBI volume, host running U-Boot under sandbox, ...) and
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ignore the ``<dev[:part]>`` field, which may be given as ``-``. So
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``load <iface> - <addr> <filename>`` works.
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semihosting
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Read files from the host filesystem of an attached JTAG debugger
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using the ARM semihosting protocol. Useful with OpenOCD.
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Built when ``CONFIG_SEMIHOSTING=y``.
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ubifs
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Read files from a UBIFS volume that has already been attached
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and mounted with the ``ubi part`` + ``ubifsmount`` commands.
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Built when ``CONFIG_CMD_UBIFS=y``.
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sandbox
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Read files from the host filesystem the sandbox binary is
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running under. Available on sandbox builds.
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The ``<dev[:part]>`` argument is conventionally written as ``-`` for
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these interfaces, to make it visible at the call site that the field
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is unused. The filesystem layer never looks at it.
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Example::
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=> load semihosting - ${kernel_addr_r} kernel.itb
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9437184 bytes read in 412 ms (21.8 MiB/s)
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=>
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Configuration
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-------------
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The load command is only available if CONFIG_CMD_FS_GENERIC=y.
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Return value
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------------
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The return value $? is set to 0 (true) if the file was successfully loaded
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even if the number of bytes is less then the specified length.
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If an error occurs, the return value $? is set to 1 (false).
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