| page.title=Device Specific Configuration |
| @jd:body |
| |
| <!-- |
| Copyright 2013 The Android Open Source Project |
| |
| Licensed under the Apache License, Version 2.0 (the "License"); |
| you may not use this file except in compliance with the License. |
| You may obtain a copy of the License at |
| |
| http://www.apache.org/licenses/LICENSE-2.0 |
| |
| Unless required by applicable law or agreed to in writing, software |
| distributed under the License is distributed on an "AS IS" BASIS, |
| WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| See the License for the specific language governing permissions and |
| limitations under the License. |
| --> |
| |
| <p>External storage is managed by a combination of the <code>vold</code> init |
| service and <code>MountService</code> system servic. Mounting of physical |
| external storage volumes is handled by <code>vold</code>, which performs |
| staging operations to prepare the media before exposing it to apps.</p> |
| |
| <p>For Android 4.2.2 and earlier, the device-specific <code>vold.fstab</code> |
| configuration file defines mappings from sysfs devices to filesystem mount |
| points, and each line follows this format:</p> |
| |
| <pre><code>dev_mount <label> <mount_point> <partition> <sysfs_path> [flags] |
| </code></pre> |
| |
| <ul> |
| <li><code>label</code>: Label for the volume.</li> |
| <li><code>mount_point</code>: Filesystem path where the volume should be mounted.</li> |
| <li><code>partition</code>: Partition number (1 based), or 'auto' for first usable partition.</li> |
| <li><code>sysfs_path</code>: One or more sysfs paths to devices that can provide this mount |
| point. Separated by spaces, and each must start with <code>/</code>.</li> |
| <li><code>flags</code>: Optional comma separated list of flags, must not contain <code>/</code>. |
| Possible values include <code>nonremovable</code> and <code>encryptable</code>.</li> |
| </ul> |
| |
| <p>For Android releases 4.3 and later, the various fstab files used by init, vold and |
| recovery were unified in the <code>/fstab.<device></code> file. For external |
| storage volumes that are managed by <code>vold</code>, the entries should have the |
| following format:</p> |
| <pre><code><src> <mnt_point> <type> <mnt_flags> <fs_mgr_flags> |
| </code></pre> |
| <ul> |
| <li><code>src</code>: A path under sysfs (usually mounted at /sys) to the device that |
| can provide the mount point. The path must start with <code>/</code>.</li> |
| <li><code>mount_point</code>: Filesystem path where the volume should be mounted.</li> |
| <li><code>type</code>: The type of the filesystem on the volume. For external cards, |
| this is usually <code>vfat</code>.</li> |
| <li><code>mnt_flags</code>: <code>Vold</code> ignores this field and it should be set |
| to <code>defaults</code></li> |
| <li><code>fs_mgr_flags</code>: <code>Vold</code> ignores any lines in the unified fstab |
| that do not include the <code>voldmanaged=</code> flag in this field. This flag must |
| be followed by a label describing the card, and a partition number or the word |
| <code>auto</code>. Here is an example: <code>voldmanaged=sdcard:auto</code>. |
| Other possible flags are <code>nonremovable</code>, |
| <code>encryptable=sdcard</code>, and <code>noemulatedsd</code>.</li> |
| </ul> |
| <p>External storage interactions at and above the framework level are handled |
| through <code>MountService</code>. The device-specific <code>storage_list.xml</code> configuration |
| file, typically provided through a <code>frameworks/base</code> overlay, defines the |
| attributes and constraints of storage devices. The <code><StorageList></code> element |
| contains one or more <code><storage></code> elements, exactly one of which should be marked |
| primary. <code><storage></code> attributes include:</p> |
| <ul> |
| <li><code>mountPoint</code>: filesystem path of this mount.</li> |
| <li><code>storageDescription</code>: string resource that describes this mount.</li> |
| <li><code>primary</code>: true if this mount is the primary external storage.</li> |
| <li><code>removable</code>: true if this mount has removable media, such as a physical SD |
| card.</li> |
| <li><code>emulated</code>: true if this mount is emulated and is backed by internal storage, |
| possibly using a FUSE daemon.</li> |
| <li><code>mtp-reserve</code>: number of MB of storage that MTP should reserve for free |
| storage. Only used when mount is marked as emulated.</li> |
| <li><code>allowMassStorage</code>: true if this mount can be shared via USB mass storage.</li> |
| <li><code>maxFileSize</code>: maximum file size in MB.</li> |
| </ul> |
| <p>Devices may provide external storage by emulating a case-insensitive, |
| permissionless filesystem backed by internal storage. One possible |
| implementation is provided by the FUSE daemon in <code>system/core/sdcard</code>, which can |
| be added as a device-specific <code>init.rc</code> service:</p> |
| <pre><code># virtual sdcard daemon running as media_rw (1023) |
| service sdcard /system/bin/sdcard <source_path> <dest_path> 1023 1023 |
| class late_start |
| </code></pre> |
| <p>Where <code>source_path</code> is the backing internal storage and <code>dest_path</code> is the |
| target mount point.</p> |
| <p>When configuring a device-specific <code>init.rc</code> script, the <code>EXTERNAL_STORAGE</code> |
| environment variable must be defined as the path to the primary external |
| storage. The <code>/sdcard</code> path must also resolve to the same location, possibly |
| through a symlink. If a device adjusts the location of external storage between |
| platform updates, symlinks should be created so that old paths continue working.</p> |