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Diffstat (limited to 'Documentation/power/userland-swsusp.txt')
| -rw-r--r-- | Documentation/power/userland-swsusp.txt | 64 |
1 files changed, 51 insertions, 13 deletions
diff --git a/Documentation/power/userland-swsusp.txt b/Documentation/power/userland-swsusp.txt index 64755e9285db..000556c932e9 100644 --- a/Documentation/power/userland-swsusp.txt +++ b/Documentation/power/userland-swsusp.txt @@ -9,9 +9,8 @@ done it already. Now, to use the userland interface for software suspend you need special utilities that will read/write the system memory snapshot from/to the kernel. Such utilities are available, for example, from -<http://www.sisk.pl/kernel/utilities/suspend>. You may want to have -a look at them if you are going to develop your own suspend/resume -utilities. +<http://suspend.sourceforge.net>. You may want to have a look at them if you +are going to develop your own suspend/resume utilities. The interface consists of a character device providing the open(), release(), read(), and write() operations as well as several ioctl() @@ -21,9 +20,9 @@ be read from /sys/class/misc/snapshot/dev. The device can be open either for reading or for writing. If open for reading, it is considered to be in the suspend mode. Otherwise it is -assumed to be in the resume mode. The device cannot be open for reading -and writing. It is also impossible to have the device open more than once -at a time. +assumed to be in the resume mode. The device cannot be open for simultaneous +reading and writing. It is also impossible to have the device open more than +once at a time. The ioctl() commands recognized by the device are: @@ -69,9 +68,46 @@ SNAPSHOT_FREE_SWAP_PAGES - free all swap pages allocated with SNAPSHOT_SET_SWAP_FILE - set the resume partition (the last ioctl() argument should specify the device's major and minor numbers in the old two-byte format, as returned by the stat() function in the .st_rdev - member of the stat structure); it is recommended to always use this - call, because the code to set the resume partition could be removed from - future kernels + member of the stat structure) + +SNAPSHOT_SET_SWAP_AREA - set the resume partition and the offset (in <PAGE_SIZE> + units) from the beginning of the partition at which the swap header is + located (the last ioctl() argument should point to a struct + resume_swap_area, as defined in kernel/power/power.h, containing the + resume device specification, as for the SNAPSHOT_SET_SWAP_FILE ioctl(), + and the offset); for swap partitions the offset is always 0, but it is + different to zero for swap files (please see + Documentation/swsusp-and-swap-files.txt for details). + The SNAPSHOT_SET_SWAP_AREA ioctl() is considered as a replacement for + SNAPSHOT_SET_SWAP_FILE which is regarded as obsolete. It is + recommended to always use this call, because the code to set the resume + partition may be removed from future kernels + +SNAPSHOT_S2RAM - suspend to RAM; using this call causes the kernel to + immediately enter the suspend-to-RAM state, so this call must always + be preceded by the SNAPSHOT_FREEZE call and it is also necessary + to use the SNAPSHOT_UNFREEZE call after the system wakes up. This call + is needed to implement the suspend-to-both mechanism in which the + suspend image is first created, as though the system had been suspended + to disk, and then the system is suspended to RAM (this makes it possible + to resume the system from RAM if there's enough battery power or restore + its state on the basis of the saved suspend image otherwise) + +SNAPSHOT_PMOPS - enable the usage of the pmops->prepare, pmops->enter and + pmops->finish methods (the in-kernel swsusp knows these as the "platform + method") which are needed on many machines to (among others) speed up + the resume by letting the BIOS skip some steps or to let the system + recognise the correct state of the hardware after the resume (in + particular on many machines this ensures that unplugged AC + adapters get correctly detected and that kacpid does not run wild after + the resume). The last ioctl() argument can take one of the three + values, defined in kernel/power/power.h: + PMOPS_PREPARE - make the kernel carry out the + pm_ops->prepare(PM_SUSPEND_DISK) operation + PMOPS_ENTER - make the kernel power off the system by calling + pm_ops->enter(PM_SUSPEND_DISK) + PMOPS_FINISH - make the kernel carry out the + pm_ops->finish(PM_SUSPEND_DISK) operation The device's read() operation can be used to transfer the snapshot image from the kernel. It has the following limitations: @@ -91,10 +127,12 @@ unfreeze user space processes frozen by SNAPSHOT_UNFREEZE if they are still frozen when the device is being closed). Currently it is assumed that the userland utilities reading/writing the -snapshot image from/to the kernel will use a swap partition, called the resume -partition, as storage space. However, this is not really required, as they -can use, for example, a special (blank) suspend partition or a file on a partition -that is unmounted before SNAPSHOT_ATOMIC_SNAPSHOT and mounted afterwards. +snapshot image from/to the kernel will use a swap parition, called the resume +partition, or a swap file as storage space (if a swap file is used, the resume +partition is the partition that holds this file). However, this is not really +required, as they can use, for example, a special (blank) suspend partition or +a file on a partition that is unmounted before SNAPSHOT_ATOMIC_SNAPSHOT and +mounted afterwards. These utilities SHOULD NOT make any assumptions regarding the ordering of data within the snapshot image, except for the image header that MAY be |
