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trace.c
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/* * drivers/base/power/trace.c * * Copyright (C) 2006 Linus Torvalds * * Trace facility for suspend/resume problems, when none of the * devices may be working. */ #include <linux/pm-trace.h> #include <linux/export.h> #include <linux/rtc.h> #include <asm/rtc.h> #include "power.h" /* * Horrid, horrid, horrid. * * It turns out that the _only_ piece of hardware that actually * keeps its value across a hard boot (and, more importantly, the * POST init sequence) is literally the realtime clock. * * Never mind that an RTC chip has 114 bytes (and often a whole * other bank of an additional 128 bytes) of nice SRAM that is * _designed_ to keep data - the POST will clear it. So we literally * can just use the few bytes of actual time data, which means that * we're really limited. * * It means, for example, that we can't use the seconds at all * (since the time between the hang and the boot might be more * than a minute), and we'd better not depend on the low bits of * the minutes either. * * There are the wday fields etc, but I wouldn't guarantee those * are dependable either. And if the date isn't valid, either the * hw or POST will do strange things. * * So we're left with: * - year: 0-99 * - month: 0-11 * - day-of-month: 1-28 * - hour: 0-23 * - min: (0-30)*2 * * Giving us a total range of 0-16128000 (0xf61800), ie less * than 24 bits of actual data we can save across reboots. * * And if your box can't boot in less than three minutes, * you're screwed. * * Now, almost 24 bits of data is pitifully small, so we need * to be pretty dense if we want to use it for anything nice. * What we do is that instead of saving off nice readable info, * we save off _hashes_ of information that we can hopefully * regenerate after the reboot. * * In particular, this means that we might be unlucky, and hit * a case where we have a hash collision, and we end up not * being able to tell for certain exactly which case happened. * But that's hopefully unlikely. * * What we do is to take the bits we can fit, and split them * into three parts (16*997*1009 = 16095568), and use the values * for: * - 0-15: user-settable * - 0-996: file + line number * - 0-1008: device */ #define USERHASH (16) #define FILEHASH (997) #define DEVHASH (1009) #define DEVSEED (7919) static unsigned int dev_hash_value; static int set_magic_time(unsigned int user, unsigned int file, unsigned int device) { unsigned int n = user + USERHASH*(file + FILEHASH*device); // June 7th, 2006 static struct rtc_time time = { .tm_sec = 0, .tm_min = 0, .tm_hour = 0, .tm_mday = 7, .tm_mon = 5, // June - counting from zero .tm_year = 106, .tm_wday = 3, .tm_yday = 160, .tm_isdst = 1 }; time.tm_year = (n % 100); n /= 100; time.tm_mon = (n % 12); n /= 12; time.tm_mday = (n % 28) + 1; n /= 28; time.tm_hour = (n % 24); n /= 24; time.tm_min = (n % 20) * 3; n /= 20; set_rtc_time(&time); return n ? -1 : 0; } static unsigned int read_magic_time(void) { struct rtc_time time; unsigned int val; get_rtc_time(&time); pr_info("RTC time: %2d:%02d:%02d, date: %02d/%02d/%02d\n", time.tm_hour, time.tm_min, time.tm_sec, time.tm_mon + 1, time.tm_mday, time.tm_year % 100); val = time.tm_year; /* 100 years */ if (val > 100) val -= 100; val += time.tm_mon * 100; /* 12 months */ val += (time.tm_mday-1) * 100 * 12; /* 28 month-days */ val += time.tm_hour * 100 * 12 * 28; /* 24 hours */ val += (time.tm_min / 3) * 100 * 12 * 28 * 24; /* 20 3-minute intervals */ return val; } /* * This is just the sdbm hash function with a user-supplied * seed and final size parameter. */ static unsigned int hash_string(unsigned int seed, const char *data, unsigned int mod) { unsigned char c; while ((c = *data++) != 0) { seed = (seed << 16) + (seed << 6) - seed + c; } return seed % mod; } void set_trace_device(struct device *dev) { dev_hash_value = hash_string(DEVSEED, dev_name(dev), DEVHASH); } EXPORT_SYMBOL(set_trace_device); /* * We could just take the "tracedata" index into the .tracedata * section instead. Generating a hash of the data gives us a * chance to work across kernel versions, and perhaps more * importantly it also gives us valid/invalid check (ie we will * likely not give totally bogus reports - if the hash matches, * it's not any guarantee, but it's a high _likelihood_ that * the match is valid). */ void generate_pm_trace(const void *tracedata, unsigned int user) { unsigned short lineno = *(unsigned short *)tracedata; const char *file = *(const char **)(tracedata + 2); unsigned int user_hash_value, file_hash_value; user_hash_value = user % USERHASH; file_hash_value = hash_string(lineno, file, FILEHASH); set_magic_time(user_hash_value, file_hash_value, dev_hash_value); } EXPORT_SYMBOL(generate_pm_trace); extern char __tracedata_start[], __tracedata_end[]; static int show_file_hash(unsigned int value) { int match; char *tracedata; match = 0; for (tracedata = __tracedata_start ; tracedata < __tracedata_end ; tracedata += 2 + sizeof(unsigned long)) { unsigned short lineno = *(unsigned short *)tracedata; const char *file = *(const char **)(tracedata + 2); unsigned int hash = hash_string(lineno, file, FILEHASH); if (hash != value) continue; pr_info(" hash matches %s:%u\n", file, lineno); match++; } return match; } static int show_dev_hash(unsigned int value) { int match = 0; struct list_head *entry; device_pm_lock(); entry = dpm_list.prev; while (entry != &dpm_list) { struct device * dev = to_device(entry); unsigned int hash = hash_string(DEVSEED, dev_name(dev), DEVHASH); if (hash == value) { dev_info(dev, "hash matches\n"); match++; } entry = entry->prev; } device_pm_unlock(); return match; } static unsigned int hash_value_early_read; int show_trace_dev_match(char *buf, size_t size) { unsigned int value = hash_value_early_read / (USERHASH * FILEHASH); int ret = 0; struct list_head *entry; /* * It's possible that multiple devices will match the hash and we can't * tell which is the culprit, so it's best to output them all. */ device_pm_lock(); entry = dpm_list.prev; while (size && entry != &dpm_list) { struct device *dev = to_device(entry); unsigned int hash = hash_string(DEVSEED, dev_name(dev), DEVHASH); if (hash == value) { int len = snprintf(buf, size, "%s\n", dev_driver_string(dev)); if (len > size) len = size; buf += len; ret += len; size -= len; } entry = entry->prev; } device_pm_unlock(); return ret; } static int early_resume_init(void) { hash_value_early_read = read_magic_time(); return 0; } static int late_resume_init(void) { unsigned int val = hash_value_early_read; unsigned int user, file, dev; user = val % USERHASH; val = val / USERHASH; file = val % FILEHASH; val = val / FILEHASH; dev = val /* % DEVHASH */; pr_info(" Magic number: %d:%d:%d\n", user, file, dev); show_file_hash(file); show_dev_hash(dev); return 0; } core_initcall(early_resume_init); late_initcall(late_resume_init);
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