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Change RomFS so that it can use MTD devices directly - without the intercession
of the block layer - as well as using block devices.
This permits RomFS:
(1) to use the MTD direct mapping facility available under NOMMU conditions if
the underlying device is directly accessible by the CPU (including XIP);
(2) and thus to be used when the block layer is disabled.
RomFS can be configured with support just for MTD devices, just for Block
devices or for both. If RomFS is configured for both, then it will treat
mtdblock device files as MTD backing stores, not block layer backing stores.
I tested this using a CONFIG_MMU=n CONFIG_BLOCK=n kernel running on my FRV
board with a RomFS image installed on the mtdram test device. I see my test
program being run XIP:
# cat /proc/maps
...
c0c000b0-c0c01f8c r-xs 00000000 1f:00 144 /mnt/doshm
...
GDB on the kernel can be used to show that these addresses are within the
set-aside RAM space.
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Bernd Schmidt <bernd.schmidt@analog.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
41 lines
1.4 KiB
Plaintext
41 lines
1.4 KiB
Plaintext
config ROMFS_FS
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tristate "ROM file system support"
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depends on BLOCK
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---help---
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This is a very small read-only file system mainly intended for
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initial ram disks of installation disks, but it could be used for
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other read-only media as well. Read
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<file:Documentation/filesystems/romfs.txt> for details.
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To compile this file system support as a module, choose M here: the
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module will be called romfs. Note that the file system of your
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root partition (the one containing the directory /) cannot be a
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module.
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If you don't know whether you need it, then you don't need it:
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answer N.
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config ROMFS_ON_BLOCK
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bool "Block device-backed ROM file system support" if (ROMFS_ON_MTD && EMBEDDED)
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depends on ROMFS_FS && BLOCK
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help
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This permits ROMFS to use block devices buffered through the page
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cache as the medium from which to retrieve data. It does not allow
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direct mapping of the medium.
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If unsure, answer Y.
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config ROMFS_ON_MTD
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bool "MTD-backed ROM file system support"
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depends on ROMFS_FS
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depends on MTD=y || (ROMFS_FS=m && MTD)
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help
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This permits ROMFS to use MTD based devices directly, without the
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intercession of the block layer (which may have been disabled). It
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also allows direct mapping of MTD devices through romfs files under
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NOMMU conditions if the underlying device is directly addressable by
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the CPU.
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If unsure, answer Y.
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