Handle MSDOS file systems properly. Before the change file systems

created on Windows XP (and others maybe) were not detected.
We detected only those created with newfs_msdos(8).

Submitted by:		Tobias Reifenberger <treif@mayn.de>
style(9)ified by:	pjd

2 files changed, 295 insertions, 34 deletions

diff --git a/sys/geom/label/g_label_msdosfs.c b/sys/geom/label/g_label_msdosfs.c
index 5e40bd9..6137de9 100644
--- a/sys/geom/label/g_label_msdosfs.c
+++ b/sys/geom/label/g_label_msdosfs.c
@@ -1,5 +1,6 @@
 /*-
  * Copyright (c) 2004 Pawel Jakub Dawidek <pjd@FreeBSD.org>
+ * Copyright (c) 2006 Tobias Reifenberger
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -34,57 +35,171 @@ __FBSDID("$FreeBSD$");
 
 #include <geom/geom.h>
 #include <geom/label/g_label.h>
+#include <geom/label/g_label_msdosfs.h>
 
 #define G_LABEL_MSDOSFS_DIR	"msdosfs"
-
-#define	FAT12	"FAT12   "
-#define	FAT16	"FAT16   "
-#define	FAT32	"FAT32   "
-#define	VOLUME_LEN	11
-#define NO_NAME "NO NAME    "
-
+#define LABEL_NO_NAME		"NO NAME    "
 
 static void
 g_label_msdosfs_taste(struct g_consumer *cp, char *label, size_t size)
 {
 	struct g_provider *pp;
-	char *sector, *volume;
-	int i;
+	FAT_BSBPB *pfat_bsbpb;
+	FAT32_BSBPB *pfat32_bsbpb;
+	FAT_DES *pfat_entry;
+	uint8_t *sector0, *sector;
+	uint32_t i;
 
 	g_topology_assert_not();
 	pp = cp->provider;
-	label[0] = '\0';
+	sector0 = NULL;
+	sector = NULL;
+	bzero(label, size);
 
-	sector = (char *)g_read_data(cp, 0, pp->sectorsize, NULL);
-	if (sector == NULL)
+	/* Check if the sector size of the medium is a valid FAT sector size. */
+	switch(pp->sectorsize) {
+	case 512:
+	case 1024:
+	case 2048:
+	case 4096:
+		break;
+	default:
+		G_LABEL_DEBUG(1, "MSDOSFS: %s: sector size %d not compatible.",
+		    pp->name, pp->sectorsize);
 		return;
-	if (strncmp(sector + 0x36, FAT12, strlen(FAT12)) == 0) {
-		G_LABEL_DEBUG(1, "MSDOS (FAT12) file system detected on %s.",
+	}
+
+	/* Load 1st sector with boot sector and boot parameter block. */
+	sector0 = (uint8_t *)g_read_data(cp, 0, pp->sectorsize, NULL);
+	if (sector0 == NULL)
+		return;
+
+	/* Check for the FAT boot sector signature. */
+	if (sector0[510] != 0x55 || sector0[511] != 0xaa) {
+		G_LABEL_DEBUG(1, "MSDOSFS: %s: no FAT signature found.",
 		    pp->name);
-		volume = sector + 0x2b;
-	} else if (strncmp(sector + 0x36, FAT16, strlen(FAT16)) == 0) {
-		G_LABEL_DEBUG(1, "MSDOS (FAT16) file system detected on %s.",
+		goto error;
+	}
+
+
+	/*
+	 * Test if this is really a FAT volume and determine the FAT type.
+	 */
+
+	pfat_bsbpb = (FAT_BSBPB *)sector0;
+	pfat32_bsbpb = (FAT32_BSBPB *)sector0;
+
+	if (UINT16BYTES(pfat_bsbpb->BPB_FATSz16) != 0) {
+		/*
+		 * If the BPB_FATSz16 field is not zero and the string "FAT" is
+		 * at the right place, this should be a FAT12 or FAT16 volume.
+		 */
+		if (strncmp(pfat_bsbpb->BS_FilSysType, "FAT", 3) != 0) {
+			G_LABEL_DEBUG(1,
+			    "MSDOSFS: %s: FAT12/16 volume not valid.",
+			    pp->name);
+			goto error;
+		}
+		G_LABEL_DEBUG(1, "MSDOSFS: %s: FAT12/FAT16 volume detected.",
 		    pp->name);
-		volume = sector + 0x2b;
-	} else if (strncmp(sector + 0x52, FAT32, strlen(FAT32)) == 0) {
-		G_LABEL_DEBUG(1, "MSDOS (FAT32) file system detected on %s.",
+
+		/* A volume with no name should have "NO NAME    " as label. */
+		if (strncmp(pfat_bsbpb->BS_VolLab, LABEL_NO_NAME,
+		    sizeof(pfat_bsbpb->BS_VolLab)) == 0) {
+			G_LABEL_DEBUG(1,
+			    "MSDOSFS: %s: FAT12/16 volume has no name.",
+			    pp->name);
+			goto error;
+		}
+		strlcpy(label, pfat_bsbpb->BS_VolLab,
+		    MIN(size, sizeof(pfat_bsbpb->BS_VolLab) + 1));
+	} else if (UINT32BYTES(pfat32_bsbpb->BPB_FATSz32) != 0) {
+		uint32_t fat_FirstDataSector, fat_BytesPerSector, offset;
+
+		/*
+		 * If the BPB_FATSz32 field is not zero and the string "FAT" is
+		 * at the right place, this should be a FAT32 volume.
+		 */
+		if (strncmp(pfat32_bsbpb->BS_FilSysType, "FAT", 3) != 0) {
+			G_LABEL_DEBUG(1, "MSDOSFS: %s: FAT32 volume not valid.",
+			    pp->name);
+			goto error;
+		}
+		G_LABEL_DEBUG(1, "MSDOSFS: %s: FAT32 volume detected.",
 		    pp->name);
-		volume = sector + 0x47;
+
+		/*
+		 * If the volume label is not "NO NAME    " we're done.
+		 */
+		if (strncmp(pfat32_bsbpb->BS_VolLab, LABEL_NO_NAME,
+		    sizeof(pfat32_bsbpb->BS_VolLab)) != 0) {
+			strlcpy(label, pfat32_bsbpb->BS_VolLab,
+			    MIN(size, sizeof(pfat32_bsbpb->BS_VolLab) + 1));
+			goto endofchecks;
+		}
+
+		/*
+		 * If the volume label "NO NAME    " is in the boot sector, the
+		 * label of FAT32 volumes may be stored as a special entry in
+		 * the root directory.
+		 */
+		fat_FirstDataSector =
+		    UINT16BYTES(pfat32_bsbpb->BPB_RsvdSecCnt) +
+		    (pfat32_bsbpb->BPB_NumFATs *
+		     UINT32BYTES(pfat32_bsbpb->BPB_FATSz32));
+		fat_BytesPerSector = UINT16BYTES(pfat32_bsbpb->BPB_BytsPerSec);
+			
+		G_LABEL_DEBUG(2,
+		    "MSDOSFS: FAT_FirstDataSector=0x%x, FAT_BytesPerSector=%d",
+		    fat_FirstDataSector, fat_BytesPerSector);
+
+		for (offset = fat_BytesPerSector * fat_FirstDataSector;;
+		    offset += fat_BytesPerSector) {
+			sector = (uint8_t *)g_read_data(cp, offset,
+			    fat_BytesPerSector, NULL);
+			if (sector == NULL)
+				goto error;
+
+			pfat_entry = (FAT_DES *)sector;
+			do {
+				/* No more entries available. */
+				if (pfat_entry->DIR_Name[0] == 0) {
+					G_LABEL_DEBUG(1, "MSDOSFS: %s: "
+					    "FAT32 volume has no name.",
+					    pp->name);
+					goto error;
+				}
+
+				/* Skip empty or long name entries. */
+				if (pfat_entry->DIR_Name[0] == 0xe5 ||
+				    (pfat_entry->DIR_Attr &
+				     FAT_DES_ATTR_LONG_NAME) ==
+				    FAT_DES_ATTR_LONG_NAME) {
+					continue;
+				}
+
+				/*
+				 * The name of the entry is the volume label if
+				 * ATTR_VOLUME_ID is set.
+				 */
+				if (pfat_entry->DIR_Attr &
+				    FAT_DES_ATTR_VOLUME_ID) {
+					strlcpy(label, pfat_entry->DIR_Name,
+					    MIN(size,
+					    sizeof(pfat_bsbpb->BS_VolLab) + 1));
+					goto endofchecks;
+				}
+			} while((uint8_t *)(++pfat_entry) <
+			    (uint8_t *)(sector + fat_BytesPerSector));
+			g_free(sector);
+		}
 	} else {
-		g_free(sector);
-		return;
-	}
-	if (strncmp(volume, NO_NAME, VOLUME_LEN) == 0) {
-		g_free(sector);
-		return;
-	}
-	if (volume[0] == '\0') {
-		g_free(sector);
-		return;
+		G_LABEL_DEBUG(1, "MSDOSFS: %s: no FAT volume detected.",
+		    pp->name);
+		goto error;
 	}
-	bzero(label, size);
-	strlcpy(label, volume, MIN(size, VOLUME_LEN));
-	g_free(sector);
+
+endofchecks:
 	for (i = size - 1; i > 0; i--) {
 		if (label[i] == '\0')
 			continue;
@@ -93,6 +208,12 @@ g_label_msdosfs_taste(struct g_consumer *cp, char *label, size_t size)
 		else
 			break;
 	}
+
+error:
+	if (sector0 != NULL)
+		g_free(sector0);
+	if (sector != NULL)
+		g_free(sector);
 }
 
 const struct g_label_desc g_label_msdosfs = {
diff --git a/sys/geom/label/g_label_msdosfs.h b/sys/geom/label/g_label_msdosfs.h
new file mode 100644
index 0000000..761461b
--- /dev/null
+++ b/sys/geom/label/g_label_msdosfs.h
@@ -0,0 +1,140 @@
+/*-
+ * Copyright (c) 2006 Tobias Reifenberger
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * $FreeBSD$
+ */
+
+#include <sys/types.h>
+
+/*
+ * Conversion macros for little endian encoded unsigned integers
+ * in byte streams to the local unsigned integer format.
+ */
+#define UINT16BYTES(p) ((uint32_t)((p)[0] + (256*(p)[1])))
+#define UINT32BYTES(p) ((uint32_t)((p)[0] + (256*(p)[1]) +		\
+	    (65536*(p)[2]) + (16777216*(p)[3])))
+
+/*
+ * All following structures are according to:
+ * 
+ * Microsoft Extensible Firmware Initiative FAT32 File System Specification
+ * FAT: General Overview of On-Disk Format
+ * Version 1.03, December 6, 2000
+ * Microsoft Corporation
+ */
+
+/*
+ * FAT boot sector and boot parameter block for
+ * FAT12 and FAT16 volumes
+ */
+typedef struct fat_bsbpb {
+	/* common fields */
+	uint8_t BS_jmpBoot[3];
+	uint8_t BS_OEMName[8];
+	uint8_t BPB_BytsPerSec[2];
+	uint8_t BPB_SecPerClus;
+	uint8_t BPB_RsvdSecCnt[2];
+	uint8_t BPB_NumFATs;
+	uint8_t BPB_RootEntCnt[2];
+	uint8_t BPB_TotSec16[2];
+	uint8_t BPB_Media;
+	uint8_t BPB_FATSz16[2];
+	uint8_t BPB_SecPerTrack[2];
+	uint8_t BPB_NumHeads[2];
+	uint8_t BPB_HiddSec[4];
+	uint8_t BPB_TotSec32[4];
+	/* FAT12/FAT16 only fields */
+	uint8_t BS_DrvNum;
+	uint8_t BS_Reserved1;
+	uint8_t BS_BootSig;
+	uint8_t BS_VolID[4];
+	uint8_t BS_VolLab[11];
+	uint8_t BS_FilSysType[8];
+} FAT_BSBPB; /* 62 bytes */
+
+/* 
+ * FAT boot sector and boot parameter block for
+ * FAT32 volumes
+ */
+typedef struct fat32_bsbpb {
+	/* common fields */
+	uint8_t BS_jmpBoot[3];
+	uint8_t BS_OEMName[8];
+	uint8_t BPB_BytsPerSec[2];
+	uint8_t BPB_SecPerClus;
+	uint8_t BPB_RsvdSecCnt[2];
+	uint8_t BPB_NumFATs;
+	uint8_t BPB_RootEntCnt[2];
+	uint8_t BPB_TotSec16[2];
+	uint8_t BPB_Media;
+	uint8_t BPB_FATSz16[2];
+	uint8_t BPB_SecPerTrack[2];
+	uint8_t BPB_NumHeads[2];
+	uint8_t BPB_HiddSec[4];
+	uint8_t BPB_TotSec32[4];
+	/* FAT32 only fields */
+	uint8_t BPB_FATSz32[4];
+	uint8_t BPB_ExtFlags[2];
+	uint8_t BPB_FSVer[2];
+	uint8_t BPB_RootClus[4];
+	uint8_t BPB_FSInfo[2];
+	uint8_t BPB_BkBootSec[2];
+	uint8_t BPB_Reserved[12];
+	uint8_t BS_DrvNum;
+	uint8_t BS_Reserved1;
+	uint8_t BS_BootSig;
+	uint8_t BS_VolID[4];
+	uint8_t BS_VolLab[11];
+	uint8_t BS_FilSysType[8];
+} FAT32_BSBPB; /* 90 bytes */
+
+/* 
+ * FAT directory entry structure
+ */
+#define	FAT_DES_ATTR_READ_ONLY	0x01
+#define	FAT_DES_ATTR_HIDDEN	0x02
+#define	FAT_DES_ATTR_SYSTEM	0x04
+#define	FAT_DES_ATTR_VOLUME_ID	0x08
+#define	FAT_DES_ATTR_DIRECTORY	0x10
+#define	FAT_DES_ATTR_ARCHIVE	0x20
+#define	FAT_DES_ATTR_LONG_NAME	(FAT_DES_ATTR_READ_ONLY |		\
+				 FAT_DES_ATTR_HIDDEN |			\
+				 FAT_DES_ATTR_SYSTEM |			\
+				 FAT_DES_ATTR_VOLUME_ID)
+
+typedef struct fat_des {
+	uint8_t DIR_Name[11];
+	uint8_t DIR_Attr;
+	uint8_t DIR_NTRes;
+	uint8_t DIR_CrtTimeTenth;
+	uint8_t DIR_CrtTime[2];
+	uint8_t DIR_CrtDate[2];
+	uint8_t DIR_LstAccDate[2];
+	uint8_t DIR_FstClusHI[2];
+	uint8_t DIR_WrtTime[2];
+	uint8_t DIR_WrtDate[2];
+	uint8_t DIR_FstClusLO[2];
+	uint8_t DIR_FileSize[4];
+} FAT_DES;