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62 lines
2.5 KiB
Markdown
62 lines
2.5 KiB
Markdown
# The eXecute In-Place File System
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## Description
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`xipfs` is a file system designed to streamline post-issuance software
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deployment. `xipfs` allows direct execution of programs from flash
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memory, eliminating the need for prior copying to RAM. This approach
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conserves memory space and accelerates boot times, as the
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microcontroller can run code directly from storage memory without
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preloading into RAM.
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The `xipfs` structure is based on a linked list, where each file
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occupies at least one flash memory page. To prevent fragmentation, when
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a file is deleted, subsequent files are shifted to fill the vacant
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space.
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`xipfs` is compatible with all microcontrollers featuring addressable
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flash memory and most operating systems, provided they implement the
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necessary functions to interact with the flash controller.
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## Limitations
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`xipfs` has the following limitations:
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- No journaling: `xipfs` doesn't provide journaling. Without journaling,
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the file system cannot keep track of changes in a way that allows for
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recovery in the event of a crash or power failure. This can lead to
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data corruption and loss.
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- No checksums: `xipfs` doesn't provide checksums. The lack of checksums
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means that the file system cannot verify the integrity of files. This
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increases the risk of undetected data corruption, as there is no
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mechanism to ensure that files have not been altered or damaged.
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- Per mountpoint file system lock: `xipfs` needs a file system lock per
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mountpoint. Such a mechanism can lead to performance bottlenecks,
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as it prevents multiple threads from accessing the file system montpoint
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simultaneously.
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- Fixed file size: `xipfs` provide fixed file size. By default, a file
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created using `vfs_open(2)` has a fixed space reserved in flash that
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is the size of a flash page. This size cannot be extended later. To
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create a file larger than the fixed size of one flash page, the
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`mk(1)` command or the `xipfs_new_file(3)` function must be used.
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- Limited character set: `xipfs` supports only a subset of 7-bit ASCII
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characters, specifically `[0-9A-Za-z\/\.\-_]`.
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- Limited path length: `xipfs` maximum path length is 64 characters.
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## Tested cards
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`xipfs` is expected to be compatible with all boards that feature
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addressable NVM. However, only the `DWM1001` board has been tested and
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is confirmed to function correctly.
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## Funding
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The `xipfs` project is part of the TinyPART project funded by the
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MESRI-BMBF German-French cybersecurity program under grant agreements
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n°ANR-20-CYAL-0005 and 16KIS1395K.
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