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Document inode_checkperm / inode_checkpathperm, mountpoint traverse vs open semantics, and the optional mountpt_operations.permission hook in file_permission.rst. Signed-off-by: Abhishek Mishra <mishra.abhishek2808@gmail.com>
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=====
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TMPFS
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=====
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NuttX TMPFS file system is a tiny dynamic RAM based file system.
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It can be enabled by adding ``CONFIG_FS_TMPFS=y`` to the configuration at build time.
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At runtime, simply use ``mount -t tmpfs /tmp`` to have a ``/tmp`` folder backed by TMPFS, then files and folders can be created under that folder.
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Be aware that TMPFS is backed by kernel memory thus don't expect to store big files on it and its size is limited by free kernel memory.
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We can watch the size of TMPFS with ``df -h`` command, especially you can see the ``Size`` column of TMPFS changes when files are added or removed in the TMPFS folder. Changes in TMPFS size is always reflected by reverse changes of free kernel memory size.
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Permissions
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===========
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When ``CONFIG_FS_PERMISSION`` is enabled, tmpfs stores per-object owner, group,
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and mode and enforces them on path operations inside the volume. It also
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implements the optional ``mountpt_operations.permission`` hook.
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Access into the mount from the pseudoFS is gated by the VFS (parent and
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mountpoint ``X_OK``). See :ref:`file-permission`.
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