hibernate . code trace

echo disk > /sys/power/state 收到的是
kernek/power/main.c : static ssize_t state_store(struct kobject *kobj, struct kobj_attribute *attr, const char *buf, size_t n) suspend to disk 部份超快，就.. if (len == 4 && !strncmp(buf, "disk", len)) { error = hibernate(); goto Exit; } 直接 call kernel/power/hibernate.c 的 hibernate( )

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snapshot_device_available 被用作 snaphot 的 mutex，初始是 1，使用時 -1。
也就是說： 1 可用，0 不行。
所以 kernel code 要操作 snapshot 時，都要先作: atomic_add_unless(&snapshot_device_available, -1 ,0) 用來確認 snaphot_device_available 是不是 1 (available)，
再繼續動作。

實際上依靠 snaphost_device_avaiable 的 function 有：

1. hibernate()
2. software_resume( )
3. snapshot_open( ) -- user interface of device "snapshot'

pm_notifier_call_chain : call blocking_notifier_call_chain( ).
好像有以下幾個 chain:

1. PM_HIBERNATION_PREPARE
2. PM_POST_HIBERNATION
3. PM_RESTORE_PREPARE
4. PM_POST_RESTORE

定義在：notifier.h /* Hibernation and suspend events */ #define PM_HIBERNATION_PREPARE 0x0001 /* Going to hibernate */ #define PM_POST_HIBERNATION 0x0002 /* Hibernation finished */ #define PM_SUSPEND_PREPARE 0x0003 /* Going to suspend the system */ #define PM_POST_SUSPEND 0x0004 /* Suspend finished */ #define PM_RESTORE_PREPARE 0x0005 /* Going to restore a saved image */ #define PM_POST_RESTORE 0x0006 /* Restore failed */
RCU : Read-Copy-Update

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static int orig_fgconsole, orig_kmsg; int pm_prepare_console(void) { orig_fgconsole = vt_move_to_console(SUSPEND_CONSOLE, 1); if (orig_fgconsole < 0) return 1; orig_kmsg = vt_kmsg_redirect(SUSPEND_CONSOLE); return 0; } void pm_restore_console(void) { if (orig_fgconsole >= 0) { vt_move_to_console(orig_fgconsole, 0); vt_kmsg_redirect(orig_kmsg); } }