48 	u_char block[DOSBOOTBLOCKSIZE];  in readboot()  local
52 	if ((size_t)read(dosfs, block, sizeof block) != sizeof block) {  in readboot()
53 		perr("could not read boot block");  in readboot()
57 	if (block[510] != 0x55 || block[511] != 0xaa) {  in readboot()
58 		pfatal("Invalid signature in boot block: %02x%02x",  in readboot()
59 		    block[511], block[510]);  in readboot()
66 	/* Decode BIOS Parameter Block */  in readboot()
69 	boot->bpbBytesPerSec = block[11] + (block[12] << 8);  in readboot()
78 	boot->bpbSecPerClust = block[13];  in readboot()
85 	boot->bpbResSectors = block[14] + (block[15] << 8);  in readboot()
93 	boot->bpbFATs = block[16];  in readboot()
100 	boot->bpbRootDirEnts = block[17] + (block[18] << 8);  in readboot()
107 	boot->bpbSectors = block[19] + (block[20] << 8);  in readboot()
115 	boot->bpbMedia = block[21];  in readboot()
118 	boot->bpbFATsmall = block[22] + (block[23] << 8);  in readboot()
126 	boot->SecPerTrack = block[24] + (block[25] << 8);  in readboot()
127 	boot->bpbHeads = block[26] + (block[27] << 8);  in readboot()
130 	boot->bpbHiddenSecs = block[28] + (block[29] << 8) +  in readboot()
131 	    (block[30] << 16) + (block[31] << 24);  in readboot()
134 	boot->bpbHugeSectors = block[32] + (block[33] << 8) +  in readboot()
135 	    (block[34] << 16) + (block[35] << 24);  in readboot()
155 		if (!memcmp(&block[3], "EXFAT   ", 8)) {  in readboot()
161 		boot->FATsecs = block[36] + (block[37] << 8)  in readboot()
162 				+ (block[38] << 16) + (block[39] << 24);  in readboot()
164 		if (block[40] & 0x80)  in readboot()
165 			boot->ValidFat = block[40] & 0x0f;  in readboot()
168 		if (block[42] || block[43]) {  in readboot()
170 			       block[43], block[42]);  in readboot()
179 		boot->bpbRootClust = block[44] + (block[45] << 8)  in readboot()
180 			       + (block[46] << 16) + (block[47] << 24);  in readboot()
183 		boot->bpbFSInfo = block[48] + (block[49] << 8);  in readboot()
185 		/* Sector number of the backup boot block, ignored */  in readboot()
186 		boot->bpbBackup = block[50] + (block[51] << 8);  in readboot()
191 			 * Either the BIOS Parameter Block has been corrupted,  in readboot()
195 			pfatal("Invalid FAT32 Extended BIOS Parameter Block");  in readboot()
199 		/* Read in and verify the FSInfo block */  in readboot()
203 			perr("could not read fsinfo block");  in readboot()
216 			pwarn("Invalid signature in fsinfo block\n");  in readboot()
238 			/* We appear to have a valid FSInfo block, decode */  in readboot()
344 		perr("could not read fsinfo block");  in writefsinfo()
366 	 * support for FAT32) doesn't maintain the FSINFO block  in writefsinfo()
369 	 * Therefore, we handle the FSINFO block only informally,  in writefsinfo()