Linux显示开机logo的函数调用：
1 register_framebuffer 2 ---> do_register_framebuffer 3 ---> fb_notifier_call_chain，传递参数FB_EVENT_FB_REGISTERED和还有fb_info的event结构 4 ---> blocking_notifier_call_chain 5 ---> __blocking_notifier_call_chain 6 ---> notifier_call_chain 7 8 --> fbcon_event_notify 9 ---> fbcon_fb_registered 10 ---> do_fbcon_takeover 11 ---> do_take_over_console 12 ---> do_bind_con_driver 13 ---> visual_init 14 ---> fbcon_init 15 ---> fbcon_prepare_logo 16 ---> fb_prepare_logo 17 ---> fb_find_logo 18 ---> update_screen 19 ---> redraw_screen 20 ---> fbcon_switch 21 ---> fb_show_logo 22 ---> fb_show_logo_line 23 ---> fb_do_show_logo
获取logo：
其中获取logo数据是在fb_find_logo中完成的：
/* logo's are marked __initdata. Use __ref to tell * modpost that it is intended that this function uses data * marked __initdata. */ const struct linux_logo * __ref fb_find_logo(int depth) { const struct linux_logo *logo = NULL; if (nologo || logos_freed) return NULL; if (depth >= 1) { #ifdef CONFIG_LOGO_LINUX_MONO /* Generic Linux logo */ logo = &logo_linux_mono; #endif #ifdef CONFIG_LOGO_SUPERH_MONO /* SuperH Linux logo */ logo = &logo_superh_mono; #endif } if (depth >= 4) { #ifdef CONFIG_LOGO_LINUX_VGA16 /* Generic Linux logo */ logo = &logo_linux_vga16; #endif #ifdef CONFIG_LOGO_BLACKFIN_VGA16 /* Blackfin processor logo */ logo = &logo_blackfin_vga16; #endif #ifdef CONFIG_LOGO_SUPERH_VGA16 /* SuperH Linux logo */ logo = &logo_superh_vga16; #endif } if (depth >= 8) { #ifdef CONFIG_LOGO_LINUX_CLUT224 /* Generic Linux logo */ logo = &logo_linux_clut224; #endif #ifdef CONFIG_LOGO_BLACKFIN_CLUT224 /* Blackfin Linux logo */ logo = &logo_blackfin_clut224; #endif #ifdef CONFIG_LOGO_DEC_CLUT224 /* DEC Linux logo on MIPS/MIPS64 or ALPHA */ logo = &logo_dec_clut224; #endif #ifdef CONFIG_LOGO_MAC_CLUT224 /* Macintosh Linux logo on m68k */ if (MACH_IS_MAC) logo = &logo_mac_clut224; #endif #ifdef CONFIG_LOGO_PARISC_CLUT224 /* PA-RISC Linux logo */ logo = &logo_parisc_clut224; #endif #ifdef CONFIG_LOGO_SGI_CLUT224 /* SGI Linux logo on MIPS/MIPS64 */ logo = &logo_sgi_clut224; #endif #ifdef CONFIG_LOGO_SUN_CLUT224 /* Sun Linux logo */ logo = &logo_sun_clut224; #endif #ifdef CONFIG_LOGO_SUPERH_CLUT224 /* SuperH Linux logo */ logo = &logo_superh_clut224; #endif #ifdef CONFIG_LOGO_M32R_CLUT224 /* M32R Linux logo */ logo = &logo_m32r_clut224; #endif } return logo; }
以logo_linux_clut224为例，它是内核根据drivers/video/logo/logo_linux_clut224.ppm生成的(具体参考drivers/video/logo/Makefile)，首先内核使用scripts/pnmtologo对logo_linux_clut224.ppm进行处理，生成名为logo_linux_clut224.c，其中含有上面的结构：
/* * DO NOT EDIT THIS FILE! * * It was automatically generated from drivers/video/logo/logo_linux_clut224.ppm * * Linux logo logo_linux_clut224 */ #include <linux/linux_logo.h> static unsigned char logo_linux_clut224_data[] __initdata = { 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, ... ... }; const struct linux_logo logo_linux_clut224 __initconst = { .type = LINUX_LOGO_CLUT224, .width = 80, .height = 80, .clutsize = 187, .clut = logo_linux_clut224_clut, .data = logo_linux_clut224_data };
显示logo是在fb_show_logo_line中完成的：
int fb_show_logo(struct fb_info *info, int rotate) { int y; y = fb_show_logo_line(info, rotate, fb_logo.logo, 0, num_online_cpus()); y = fb_show_extra_logos(info, y, rotate); return y; }
上面在调用fb_show_logo_line时传入的最后一个参数表示连续输出几份logo，可以看到这里传入的是num_online_cpus()，即获取当前处于online的cpu的个数，所以如果是4核的cpu，那么开机会显示四只可爱的小企鹅：
完。
