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arm64 devicetree 組合中的boot_command_line的獲取

>setup_arch(&command_line)->setup_machine_fdt(__fdt_pointer);需要注意的是*command_line 是指向到 boot_command_line;而boot_command_line是一個靜態(tài)數(shù)組，在arm64的環(huán)境下是2048，也就是說bootloader傳遞給kernel的commandline超過2048就要修改kernel源代碼加這個數(shù)組加大。 char __initdata boot_command_line[COMMAND_LINE_SIZE]; 注意這個__fdt_pointer 是bootloader傳遞過來的，代表devicetree在內(nèi)存中的地址 static void __init setup_machine_fdt(phys_addr_t dt_phys) {     void *dt_virt = fixmap_remap_fdt(dt_phys);     if (!dt_virt || !early_init_dt_scan(dt_virt)) {         PR_crit("\n"             "Error: invalid device tree blob at physical address %pa (virtual address 0x%p)\n"             "The dtb must be 8-byte aligned and must not exceed 2 MB in size\n"             "\nPlease check your bootloader.",             &dt_phys, dt_virt);         while (true)             cpu_relax();     } } 在setup_machine_fdt 中現(xiàn)將代表devicetree的物理地址轉(zhuǎn)成虛擬地址，然后調(diào)用early_init_dt_scan 來掃描devicetree中的chosen節(jié)點，其中 chosen節(jié)點就表示bootloader傳遞給kernel的commandline early_init_dt_scan->early_init_dt_scan_nodes void __init early_init_dt_scan_nodes(void) {     /* Retrieve various information from the /chosen node */     of_scan_flat_dt(early_init_dt_scan_chosen, boot_command_line);     /* Initialize {size,address}-cells info */     of_scan_flat_dt(early_init_dt_scan_root, NULL);     /* Setup memory, calling early_init_dt_add_memory_arch */     of_scan_flat_dt(early_init_dt_scan_memory, NULL); } 在early_init_dt_scan_nodes 中首先調(diào)用early_init_dt_scan_chosen 來掃描chosen節(jié)點 int __init early_init_dt_scan_chosen(unsigned long node, const char *uname,                      int depth, void *data) {     int l;     const char *p;     pr_debug("search \"chosen\", depth: %d, uname: %s\n", depth, uname);     if (depth != 1 || !data ||         (strcmp(uname, "chosen") != 0 && strcmp(uname, "chosen@0") != 0))         return 0;     early_init_dt_check_for_initrd(node);     /* Retrieve command line */     p = of_get_flat_dt_prop(node, "bootargs", &l);     if (p != NULL && l > 0)         strlcpy(data, p, min((int)l, COMMAND_LINE_SIZE));     /*      * CONFIG_CMDLINE is meant to be a default in case nothing else      * managed to set the command line, unless CONFIG_CMDLINE_FORCE      * is set in which case we override whatever was found earlier.      */ #ifdef CONFIG_CMDLINE #if defined(CONFIG_CMDLINE_EXTEND)     strlcat(data, " ", COMMAND_LINE_SIZE);     strlcat(data, CONFIG_CMDLINE, COMMAND_LINE_SIZE); #elif defined(CONFIG_CMDLINE_FORCE)     strlcpy(data, CONFIG_CMDLINE, COMMAND_LINE_SIZE); #else     /* No arguments from boot loader, use kernel s  cmdl*/     if (!((char *)data)[0])         strlcpy(data, CONFIG_CMDLINE, COMMAND_LINE_SIZE); #endif #endif /* CONFIG_CMDLINE */     pr_debug("Command line is: %s\n", (char*)data);     /* break now */     return 1; } early_init_dt_scan_chosen 中**p = of_get_flat_dt_prop(node, "bootargs", &l); 得到chosen節(jié)點中的bootargs，這個就代表commandline 然后**strlcpy(data, p, min((int)l, COMMAND_LINE_SIZE));將commandline copy到boot_command_line中 devicetree 中的chosen 節(jié)點大概是下面這樣     chosen {         bootargs = "ignore_loglevel rw root=/dev/nfs ip=dhcp";         stdout-path = "serial0:115200n8";     };

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