kernel log buf dump function kmsg_dump_get_buffer()
kernel log buf dump function kmsg_dump_get_buffer()
4.19/kernel/printk/printk.c
void kmsg_dump(enum kmsg_dump_reason reason) { struct kmsg_dumper *dumper; unsigned long flags; if ((reason > KMSG_DUMP_OOPS) && !always_kmsg_dump) return; rcu_read_lock(); list_for_each_entry_rcu(dumper, &dump_list, list) { if (dumper->max_reason && reason > dumper->max_reason) continue; /* initialize iterator with data about the stored records */ dumper->active = true; logbuf_lock_irqsave(flags); dumper->cur_seq = clear_seq; dumper->cur_idx = clear_idx; dumper->next_seq = log_next_seq; dumper->next_idx = log_next_idx; logbuf_unlock_irqrestore(flags); /* invoke dumper which will iterate over records */ dumper->dump(dumper, reason); /* reset iterator */ dumper->active = false; } rcu_read_unlock(); }
bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog, char *buf, size_t size, size_t *len) { unsigned long flags; u64 seq; u32 idx; u64 next_seq; u32 next_idx; size_t l = 0; bool ret = false; if (!dumper->active) goto out; logbuf_lock_irqsave(flags); if (dumper->cur_seq < log_first_seq) { /* messages are gone, move to first available one */ dumper->cur_seq = log_first_seq; dumper->cur_idx = log_first_idx; } /* last entry */ if (dumper->cur_seq >= dumper->next_seq) { logbuf_unlock_irqrestore(flags); goto out; } /* calculate length of entire buffer */ seq = dumper->cur_seq; idx = dumper->cur_idx; while (seq < dumper->next_seq) { struct printk_log *msg = log_from_idx(idx); l += msg_print_text(msg, true, NULL, 0); idx = log_next(idx); seq++; } /* move first record forward until length fits into the buffer */ seq = dumper->cur_seq; idx = dumper->cur_idx; while (l >= size && seq < dumper->next_seq) { struct printk_log *msg = log_from_idx(idx); l -= msg_print_text(msg, true, NULL, 0); idx = log_next(idx); seq++; } /* last message in next interation */ next_seq = seq; next_idx = idx; l = 0; while (seq < dumper->next_seq) { struct printk_log *msg = log_from_idx(idx); l += msg_print_text(msg, syslog, buf + l, size - l); idx = log_next(idx); seq++; } dumper->next_seq = next_seq; dumper->next_idx = next_idx; ret = true; logbuf_unlock_irqrestore(flags); out: if (len) *len = l; return ret; } EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
下面两个变量表示kernel log buf最后一个clear log buffer后的位置(index)
dumper->cur_seq
dumper->cur_idx
下面两个变量表示kernel log buf里指向buf开头的seq、idx:
log_first_seq
log_first_idx
下面变量表示kernel log buf下一个写log的位置:
dumper->next_seq
kmsg_dump_get_buffer()函数会先计算kernel log buf目前总的size,如果这个len和此函数参数len要大,会将seq、idx前移,直到log buf size小于等于参数len,即会将会将log buf开头部分去掉,之后再将后面的log buf整体复制到函数参数buf所表示的buffer里,所以这会将kernel log buf里最新的log复制给调用者。
分类:
kernel misc
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