70 lines
3.0 KiB
ReStructuredText
70 lines
3.0 KiB
ReStructuredText
============
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Auto-Mounter
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============
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General Description
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===================
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NuttX implements an auto-mounter than can make working with SD cards or other
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removable media easier. With the auto-mounter, the file system will be
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automatically mounted when media is inserted and automatically unmounted when
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the media is removed.
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The auto is enable by selecting in the NuttX configuration::
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CONFIG_FS_AUTOMOUNTER=y
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WARNING: SD cards should never be removed without first unmounting them. This
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is to avoid data and possible corruption of the file system. Certainly this is
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the case if you are writing to the SD card at the time of the removal. If you
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use the SD card for read-only access, however, then I cannot think of any
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reason why removing the card without mounting would be harmful.
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For applications that write to the removable media, the automatic unmount is
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still beneficial (as opposed to leaving a broken mount in place) although
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should not be relied upon for a proper solution.
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Board-Specific Support
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======================
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Like many components of NuttX, the auto-mounter has a upper-half/lower-half
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architecture:
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* **Upper half** The upper half is the file ``fs/fs_automount.c``. This upper
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half performs the basic automount activities. It responds to media
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insertion and removal events by mounting and unmounting the file system on
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the media. This includes logic to handle unmount retries: The unmount cannot
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be performed while applications have open files on the media. In this case,
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the auto-mounter will periodically retry the unmount until all of the
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applications close there references to files on the non-existent media.
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* **Lower Half** The lower half is defined by a standard interface. That
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interface definition is in the header file ``include/nuttx/fs/automount.h``.
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The lower half interface provides: (1) mount information including file
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system type, block driver path, and mount point path, (2) mount and unmount
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retry delays, and (3) and callbacks to attach to and management the media
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insertion / removal interrupts.
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Example Implementation
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======================
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There is an example implementation of this lower half interface at
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``boards/arm/sama5/sama5d4-ek/src/sam_automount.c``. The ``boards/arm/sama5/sama5d4-ek/Kconfig``
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as the board-specific configuration for the auto-mounter. You can see
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the configuration settings in the ``boards/arm/sama5/sama5d4-ek/configs/nsh/defconfig``
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and ``boards/arm/sama5/sama5d4-ek/configs/nxwm/defconfig`` configuration files::
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CONFIG_SAMA5D4EK_HSMCI0_AUTOMOUNT=y
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CONFIG_SAMA5D4EK_HSMCI0_AUTOMOUNT_FSTYPE="vfat"
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CONFIG_SAMA5D4EK_HSMCI0_AUTOMOUNT_BLKDEV="/dev/mmcsd0"
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CONFIG_SAMA5D4EK_HSMCI0_AUTOMOUNT_MOUNTPOINT="/mnt/sdcard"
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CONFIG_SAMA5D4EK_HSMCI0_AUTOMOUNT_DDELAY=1000
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CONFIG_SAMA5D4EK_HSMCI0_AUTOMOUNT_UDELAY=2000
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These setting determine the values in the lower half interface. The interrupt is
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provided by a PIO pin defined in ``boards/arm/sama5/sama5d4-ek/src/sama5e4-ek.h`` and
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the implementation of the interface and callbacks is in
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``boards/arm/sama5/sama5d4-ek/src/sam_automount.c``.
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