Documentation/power/userland-swsusp.rst

13 utilities that will read/write the system memory snapshot from/to the
45 	create a snapshot of the system memory; the
48 	creating the snapshot (1) or after restoring the system memory state
49 	from it (0) (after resume the system finds itself finishing the
55 	restore the system memory state from the
57 	the system memory snapshot back to the kernel using the write()
81 	allocate a swap page from the resume partition
90 	set the resume partition and the offset (in <PAGE_SIZE>
91 	units) from the beginning of the partition at which the swap header is
96 	swap files (see Documentation/power/swsusp-and-swap-files.rst for
104 	make the kernel transition the system to the hibernation
109 	immediately enter the suspend-to-RAM state, so this call must always
111 	to use the SNAPSHOT_UNFREEZE call after the system wakes up.  This call
112 	is needed to implement the suspend-to-both mechanism in which the
113 	suspend image is first created, as though the system had been suspended
114 	to disk, and then the system is suspended to RAM (this makes it possible
115 	to resume the system from RAM if there's enough battery power or restore
121 - you cannot read() more than one virtual memory page at a time
122 - read()s across page boundaries are impossible (ie. if you read() 1/2 of
126 The device's write() operation is used for uploading the system memory snapshot
137 snapshot image from/to the kernel will use a swap partition, called the resume
138 partition, or a swap file as storage space (if a swap file is used, the resume
139 partition is the partition that holds this file).  However, this is not really
140 required, as they can use, for example, a special (blank) suspend partition or
141 a file on a partition that is unmounted before SNAPSHOT_CREATE_IMAGE and
151 resumed system may be totally unpredictable.
156 SNAPSHOT_ATOMIC_RESTORE will not succeed.  Still, this is not a fool-proof
167 1. 	If the value is 1 (ie. the system memory snapshot has just been
168 	created and the system is ready for saving it):
175 		system MUST be powered off or rebooted after the snapshot
178 		file system operations (including reads) on the file systems
180 		called.  However, it MAY mount a file system that was not
184 2.	If the value is 0 (ie. the system state has just been restored from
189 The resuming utility SHOULD NOT attempt to mount any file systems that could
191 involving such file systems.