FATFS学习（3.1）：ff.c（f_mount）

一： Mount/Unmount a Logical Drive

/*-----------------------------------------------------------------------*/
/* Mount/Unmount a Logical Drive                                         */
/*-----------------------------------------------------------------------*/

FRESULT f_mount (
	FATFS* fs,			/* Pointer to the filesystem object to be registered (NULL:unmount)*/
	const TCHAR* path,	/* Logical drive number to be mounted/unmounted */
	BYTE opt			/* Mount option: 0=Do not mount (delayed mount), 1=Mount immediately */
)
{
	FATFS *cfs;
	int vol;
	FRESULT res;
	const TCHAR *rp = path;


	/* Get volume ID (logical drive number) */
	vol = get_ldnumber(&rp);
	if (vol < 0) return FR_INVALID_DRIVE;
	cfs = FatFs[vol];			/* Pointer to the filesystem object of the volume */

	if (cfs) {					/* Unregister current filesystem object if regsitered */
		FatFs[vol] = 0;
#if FF_FS_LOCK
		clear_share(cfs);
#endif
#if FF_FS_REENTRANT				/* Discard mutex of the current volume */
		ff_mutex_delete(vol);
#endif
		cfs->fs_type = 0;		/* Invalidate the filesystem object to be unregistered */
	}

	if (fs) {					/* Register new filesystem object */
		fs->pdrv = LD2PD(vol);	/* Volume hosting physical drive */
#if FF_FS_REENTRANT				/* Create a volume mutex */
		fs->ldrv = (BYTE)vol;	/* Owner volume ID */
		if (!ff_mutex_create(vol)) return FR_INT_ERR;
#if FF_FS_LOCK
		if (SysLock == 0) {		/* Create a system mutex if needed */
			if (!ff_mutex_create(FF_VOLUMES)) {
				ff_mutex_delete(vol);
				return FR_INT_ERR;
			}
			SysLock = 1;		/* System mutex is ready */
		}
#endif
#endif
		fs->fs_type = 0;		/* Invalidate the new filesystem object */
		FatFs[vol] = fs;		/* Register new fs object */
	}

	if (opt == 0) return FR_OK;	/* Do not mount now, it will be mounted in subsequent file functions */

	res = mount_volume(&path, &fs, 0);	/* Force mounted the volume */
	LEAVE_FF(fs, res);
}

1. 函数功能

f_mount 是 FATFS 文件系统库中的核心函数，用于 挂载（注册）或卸载（注销）逻辑驱动器 的文件系统对象。具体功能包括：

• 挂载文件系统：将 FATFS 对象与逻辑驱动器关联，并初始化文件系统。

• 卸载文件系统：解除当前关联的 FATFS 对象，释放资源。

• 延迟挂载：支持注册文件系统但不立即初始化（需后续文件操作触发）。

---

2. 参数说明

参数	类型	说明
fs	FATFS*	要注册的文件系统对象指针（NULL 表示卸载当前文件系统）。
path	const TCHAR*	逻辑驱动器路径（如 "0:"），用于确定驱动器号。
opt	BYTE	挂载选项：0=延迟挂载（后续操作触发初始化），1=立即挂载。

3. 函数逻辑流程

步骤 1：获取逻辑驱动器号

vol = get_ldnumber(&rp);  // 解析路径，获取逻辑驱动器号（如 "0:"→0）
if (vol < 0) return FR_INVALID_DRIVE;

• get_ldnumber 解析路径中的逻辑驱动器号（例如 "0:" 对应 vol=0）。

• 无效路径返回 FR_INVALID_DRIVE。

---

步骤 2：卸载当前文件系统（若存在）

	cfs = FatFs[vol];			/* Pointer to the filesystem object of the volume */

	if (cfs) {					/* Unregister current filesystem object if regsitered */
		FatFs[vol] = 0;
#if FF_FS_LOCK
		clear_share(cfs);
#endif
#if FF_FS_REENTRANT				/* Discard mutex of the current volume */
		ff_mutex_delete(vol);
#endif
		cfs->fs_type = 0;		/* Invalidate the filesystem object to be unregistered */
	}

• 若当前驱动器已挂载文件系统，先释放相关资源并注销。

---

步骤 3：注册新文件系统对象（若 fs 非空）

	if (fs) {					/* Register new filesystem object */
		fs->pdrv = LD2PD(vol);	/* Volume hosting physical drive */
#if FF_FS_REENTRANT				/* Create a volume mutex */
		fs->ldrv = (BYTE)vol;	/* Owner volume ID */
		if (!ff_mutex_create(vol)) return FR_INT_ERR;
#if FF_FS_LOCK
		if (SysLock == 0) {		/* Create a system mutex if needed */
			if (!ff_mutex_create(FF_VOLUMES)) {
				ff_mutex_delete(vol);
				return FR_INT_ERR;
			}
			SysLock = 1;		/* System mutex is ready */
		}
#endif
#endif
		fs->fs_type = 0;		/* Invalidate the new filesystem object */
		FatFs[vol] = fs;		/* Register new fs object */
	}

• 将新的 FATFS 对象关联到逻辑驱动器，初始化同步机制。

---

步骤 4：立即挂载（若 opt == 1）

if (opt == 0) return FR_OK;  // 延迟挂载，直接返回
res = mount_volume(&path, &fs, 0);  // 调用底层函数初始化文件系统
LEAVE_FF(fs, res);            // 返回结果（可能释放互斥锁）

• 若选择立即挂载，调用 mount_volume 初始化文件系统（读取引导扇区、FAT表等）。

4. 关键代码段解析

资源清理与同步

• 文件锁定（FF_FS_LOCK）：
  清理文件的共享访问控制（例如多线程同时访问文件时的互斥）。

• 互斥锁（FF_FS_REENTRANT）：
  确保多线程环境下对文件系统的原子操作：

  • ff_mutex_delete(vol)：删除驱动器级锁。

  • ff_mutex_create(vol)：创建驱动器级锁。

  • SysLock：系统级全局锁，用于保护共享资源（如 FatFs 数组）。

延迟挂载（Lazy Mount）

• 若 opt=0，仅注册 FATFS 对象但不初始化，首次文件操作（如 f_open）时触发初始化。

---

5. 设计模式与技巧

模块化设计

• 分层架构：
  通过 FatFs[vol] 全局数组管理所有逻辑驱动器的文件系统对象，实现驱动器与文件系统的解耦。

• 条件编译：
  使用 FF_FS_LOCK、FF_FS_REENTRANT 等宏控制功能模块，增强代码可移植性。

资源管理

• 引用计数与无效标记：
  通过 fs->fs_type = 0 标记文件系统对象无效，防止误用已卸载的对象。

• 互斥锁生命周期：
  在注册/注销时动态创建/删除互斥锁，避免资源泄漏。

---

6. 典型应用场景

// 挂载逻辑驱动器 0
FATFS fs;
f_mount(&fs, "0:", 1);  // 立即挂载

// 卸载逻辑驱动器 0
f_mount(NULL, "0:", 0);  // 卸载

---

7. 总结

• 核心功能：管理逻辑驱动器的挂载与卸载，关联文件系统对象。

• 关键机制：资源清理、互斥锁、延迟初始化。

• 适用场景：嵌入式系统中动态挂载存储设备（如 SD 卡、USB 设备）。

• 扩展性：通过条件编译支持多种配置（如多线程安全、文件锁定）。

通过此函数，FATFS 实现了灵活的文件系统管理，适用于资源受限的嵌入式环境。

8. 引用其他函数

 Get logical drive number from path name

• get_ldnumber（const TCHAR** path）

static int get_ldnumber (	/* Returns logical drive number (-1:invalid drive number or null pointer) */
	const TCHAR** path		/* Pointer to pointer to the path name */
)
{
	const TCHAR *tp;
	const TCHAR *tt;
	TCHAR tc;
	int i;
	int vol = -1;
#if FF_STR_VOLUME_ID		/* Find string volume ID */
	const char *sp;
	char c;
#endif

	tt = tp = *path;
	if (!tp) return vol;	/* Invalid path name? */
	do {					/* Find a colon in the path */
		tc = *tt++;
	} while (!IsTerminator(tc) && tc != ':');

	if (tc == ':') {	/* DOS/Windows style volume ID? */
		i = FF_VOLUMES;
		if (IsDigit(*tp) && tp + 2 == tt) {	/* Is there a numeric volume ID + colon? */
			i = (int)*tp - '0';	/* Get the LD number */
		}
#if FF_STR_VOLUME_ID == 1	/* Arbitrary string is enabled */
		else {
			i = 0;
			do {
				sp = VolumeStr[i]; tp = *path;	/* This string volume ID and path name */
				do {	/* Compare the volume ID with path name */
					c = *sp++; tc = *tp++;
					if (IsLower(c)) c -= 0x20;
					if (IsLower(tc)) tc -= 0x20;
				} while (c && (TCHAR)c == tc);
			} while ((c || tp != tt) && ++i < FF_VOLUMES);	/* Repeat for each id until pattern match */
		}
#endif
		if (i < FF_VOLUMES) {	/* If a volume ID is found, get the drive number and strip it */
			vol = i;		/* Drive number */
			*path = tt;		/* Snip the drive prefix off */
		}
		return vol;
	}
#if FF_STR_VOLUME_ID == 2		/* Unix style volume ID is enabled */
	if (*tp == '/') {			/* Is there a volume ID? */
		while (*(tp + 1) == '/') tp++;	/* Skip duplicated separator */
		i = 0;
		do {
			tt = tp; sp = VolumeStr[i]; /* Path name and this string volume ID */
			do {	/* Compare the volume ID with path name */
				c = *sp++; tc = *(++tt);
				if (IsLower(c)) c -= 0x20;
				if (IsLower(tc)) tc -= 0x20;
			} while (c && (TCHAR)c == tc);
		} while ((c || (tc != '/' && !IsTerminator(tc))) && ++i < FF_VOLUMES);	/* Repeat for each ID until pattern match */
		if (i < FF_VOLUMES) {	/* If a volume ID is found, get the drive number and strip it */
			vol = i;		/* Drive number */
			*path = tt;		/* Snip the drive prefix off */
		}
		return vol;
	}
#endif
	/* No drive prefix is found */
#if FF_FS_RPATH != 0
	vol = CurrVol;	/* Default drive is current drive */
#else
	vol = 0;		/* Default drive is 0 */
#endif
	return vol;		/* Return the default drive */
}

 Determine logical drive number and mount the volume if needed

• FRESULT mount_volume (const TCHAR** path, FATFS** rfs, BYTE mode)

static FRESULT mount_volume (	/* FR_OK(0): successful, !=0: an error occurred */
	const TCHAR** path,			/* Pointer to pointer to the path name (drive number) */
	FATFS** rfs,				/* Pointer to pointer to the found filesystem object */
	BYTE mode					/* Desiered access mode to check write protection */
)
{
	int vol;
	FATFS *fs;
	DSTATUS stat;
	LBA_t bsect;
	DWORD tsect, sysect, fasize, nclst, szbfat;
	WORD nrsv;
	UINT fmt;


	/* Get logical drive number */
	*rfs = 0;
	vol = get_ldnumber(path);
	if (vol < 0) return FR_INVALID_DRIVE;

	/* Check if the filesystem object is valid or not */
	fs = FatFs[vol];					/* Get pointer to the filesystem object */
	if (!fs) return FR_NOT_ENABLED;		/* Is the filesystem object available? */
#if FF_FS_REENTRANT
	if (!lock_volume(fs, 1)) return FR_TIMEOUT;	/* Lock the volume, and system if needed */
#endif
	*rfs = fs;							/* Return pointer to the filesystem object */

	mode &= (BYTE)~FA_READ;				/* Desired access mode, write access or not */
	if (fs->fs_type != 0) {				/* If the volume has been mounted */
		stat = disk_status(fs->pdrv);
		if (!(stat & STA_NOINIT)) {		/* and the physical drive is kept initialized */
			if (!FF_FS_READONLY && mode && (stat & STA_PROTECT)) {	/* Check write protection if needed */
				return FR_WRITE_PROTECTED;
			}
			return FR_OK;				/* The filesystem object is already valid */
		}
	}

	/* The filesystem object is not valid. */
	/* Following code attempts to mount the volume. (find an FAT volume, analyze the BPB and initialize the filesystem object) */

	fs->fs_type = 0;					/* Invalidate the filesystem object */
	stat = disk_initialize(fs->pdrv);	/* Initialize the volume hosting physical drive */
	if (stat & STA_NOINIT) { 			/* Check if the initialization succeeded */
		return FR_NOT_READY;			/* Failed to initialize due to no medium or hard error */
	}
	if (!FF_FS_READONLY && mode && (stat & STA_PROTECT)) { /* Check disk write protection if needed */
		return FR_WRITE_PROTECTED;
	}
#if FF_MAX_SS != FF_MIN_SS				/* Get sector size (multiple sector size cfg only) */
	if (disk_ioctl(fs->pdrv, GET_SECTOR_SIZE, &SS(fs)) != RES_OK) return FR_DISK_ERR;
	if (SS(fs) > FF_MAX_SS || SS(fs) < FF_MIN_SS || (SS(fs) & (SS(fs) - 1))) return FR_DISK_ERR;
#endif

	/* Find an FAT volume on the hosting drive */
	fmt = find_volume(fs, LD2PT(vol));
	if (fmt == 4) return FR_DISK_ERR;		/* An error occurred in the disk I/O layer */
	if (fmt >= 2) return FR_NO_FILESYSTEM;	/* No FAT volume is found */
	bsect = fs->winsect;					/* Volume offset in the hosting physical drive */

	/* An FAT volume is found (bsect). Following code initializes the filesystem object */

#if FF_FS_EXFAT
	if (fmt == 1) {
		QWORD maxlba;
		DWORD so, cv, bcl, i;

		for (i = BPB_ZeroedEx; i < BPB_ZeroedEx + 53 && fs->win[i] == 0; i++) ;	/* Check zero filler */
		if (i < BPB_ZeroedEx + 53) return FR_NO_FILESYSTEM;

		if (ld_word(fs->win + BPB_FSVerEx) != 0x100) return FR_NO_FILESYSTEM;	/* Check exFAT version (must be version 1.0) */

		if (1 << fs->win[BPB_BytsPerSecEx] != SS(fs)) {	/* (BPB_BytsPerSecEx must be equal to the physical sector size) */
			return FR_NO_FILESYSTEM;
		}

		maxlba = ld_qword(fs->win + BPB_TotSecEx) + bsect;	/* Last LBA of the volume + 1 */
		if (!FF_LBA64 && maxlba >= 0x100000000) return FR_NO_FILESYSTEM;	/* (It cannot be accessed in 32-bit LBA) */

		fs->fsize = ld_dword(fs->win + BPB_FatSzEx);	/* Number of sectors per FAT */

		fs->n_fats = fs->win[BPB_NumFATsEx];			/* Number of FATs */
		if (fs->n_fats != 1) return FR_NO_FILESYSTEM;	/* (Supports only 1 FAT) */

		fs->csize = 1 << fs->win[BPB_SecPerClusEx];		/* Cluster size */
		if (fs->csize == 0)	return FR_NO_FILESYSTEM;	/* (Must be 1..32768 sectors) */

		nclst = ld_dword(fs->win + BPB_NumClusEx);		/* Number of clusters */
		if (nclst > MAX_EXFAT) return FR_NO_FILESYSTEM;	/* (Too many clusters) */
		fs->n_fatent = nclst + 2;

		/* Boundaries and Limits */
		fs->volbase = bsect;
		fs->database = bsect + ld_dword(fs->win + BPB_DataOfsEx);
		fs->fatbase = bsect + ld_dword(fs->win + BPB_FatOfsEx);
		if (maxlba < (QWORD)fs->database + nclst * fs->csize) return FR_NO_FILESYSTEM;	/* (Volume size must not be smaller than the size required) */
		fs->dirbase = ld_dword(fs->win + BPB_RootClusEx);

		/* Get bitmap location and check if it is contiguous (implementation assumption) */
		so = i = 0;
		for (;;) {	/* Find the bitmap entry in the root directory (in only first cluster) */
			if (i == 0) {
				if (so >= fs->csize) return FR_NO_FILESYSTEM;	/* Not found? */
				if (move_window(fs, clst2sect(fs, (DWORD)fs->dirbase) + so) != FR_OK) return FR_DISK_ERR;
				so++;
			}
			if (fs->win[i] == ET_BITMAP) break;			/* Is it a bitmap entry? */
			i = (i + SZDIRE) % SS(fs);	/* Next entry */
		}
		bcl = ld_dword(fs->win + i + 20);				/* Bitmap cluster */
		if (bcl < 2 || bcl >= fs->n_fatent) return FR_NO_FILESYSTEM;	/* (Wrong cluster#) */
		fs->bitbase = fs->database + fs->csize * (bcl - 2);	/* Bitmap sector */
		for (;;) {	/* Check if bitmap is contiguous */
			if (move_window(fs, fs->fatbase + bcl / (SS(fs) / 4)) != FR_OK) return FR_DISK_ERR;
			cv = ld_dword(fs->win + bcl % (SS(fs) / 4) * 4);
			if (cv == 0xFFFFFFFF) break;				/* Last link? */
			if (cv != ++bcl) return FR_NO_FILESYSTEM;	/* Fragmented bitmap? */
		}

#if !FF_FS_READONLY
		fs->last_clst = fs->free_clst = 0xFFFFFFFF;		/* Initialize cluster allocation information */
#endif
		fmt = FS_EXFAT;			/* FAT sub-type */
	} else
#endif	/* FF_FS_EXFAT */
	{
		if (ld_word(fs->win + BPB_BytsPerSec) != SS(fs)) return FR_NO_FILESYSTEM;	/* (BPB_BytsPerSec must be equal to the physical sector size) */

		fasize = ld_word(fs->win + BPB_FATSz16);		/* Number of sectors per FAT */
		if (fasize == 0) fasize = ld_dword(fs->win + BPB_FATSz32);
		fs->fsize = fasize;

		fs->n_fats = fs->win[BPB_NumFATs];				/* Number of FATs */
		if (fs->n_fats != 1 && fs->n_fats != 2) return FR_NO_FILESYSTEM;	/* (Must be 1 or 2) */
		fasize *= fs->n_fats;							/* Number of sectors for FAT area */

		fs->csize = fs->win[BPB_SecPerClus];			/* Cluster size */
		if (fs->csize == 0 || (fs->csize & (fs->csize - 1))) return FR_NO_FILESYSTEM;	/* (Must be power of 2) */

		fs->n_rootdir = ld_word(fs->win + BPB_RootEntCnt);	/* Number of root directory entries */
		if (fs->n_rootdir % (SS(fs) / SZDIRE)) return FR_NO_FILESYSTEM;	/* (Must be sector aligned) */

		tsect = ld_word(fs->win + BPB_TotSec16);		/* Number of sectors on the volume */
		if (tsect == 0) tsect = ld_dword(fs->win + BPB_TotSec32);

		nrsv = ld_word(fs->win + BPB_RsvdSecCnt);		/* Number of reserved sectors */
		if (nrsv == 0) return FR_NO_FILESYSTEM;			/* (Must not be 0) */

		/* Determine the FAT sub type */
		sysect = nrsv + fasize + fs->n_rootdir / (SS(fs) / SZDIRE);	/* RSV + FAT + DIR */
		if (tsect < sysect) return FR_NO_FILESYSTEM;	/* (Invalid volume size) */
		nclst = (tsect - sysect) / fs->csize;			/* Number of clusters */
		if (nclst == 0) return FR_NO_FILESYSTEM;		/* (Invalid volume size) */
		fmt = 0;
		if (nclst <= MAX_FAT32) fmt = FS_FAT32;
		if (nclst <= MAX_FAT16) fmt = FS_FAT16;
		if (nclst <= MAX_FAT12) fmt = FS_FAT12;
		if (fmt == 0) return FR_NO_FILESYSTEM;

		/* Boundaries and Limits */
		fs->n_fatent = nclst + 2;						/* Number of FAT entries */
		fs->volbase = bsect;							/* Volume start sector */
		fs->fatbase = bsect + nrsv; 					/* FAT start sector */
		fs->database = bsect + sysect;					/* Data start sector */
		if (fmt == FS_FAT32) {
			if (ld_word(fs->win + BPB_FSVer32) != 0) return FR_NO_FILESYSTEM;	/* (Must be FAT32 revision 0.0) */
			if (fs->n_rootdir != 0) return FR_NO_FILESYSTEM;	/* (BPB_RootEntCnt must be 0) */
			fs->dirbase = ld_dword(fs->win + BPB_RootClus32);	/* Root directory start cluster */
			szbfat = fs->n_fatent * 4;					/* (Needed FAT size) */
		} else {
			if (fs->n_rootdir == 0)	return FR_NO_FILESYSTEM;	/* (BPB_RootEntCnt must not be 0) */
			fs->dirbase = fs->fatbase + fasize;			/* Root directory start sector */
			szbfat = (fmt == FS_FAT16) ?				/* (Needed FAT size) */
				fs->n_fatent * 2 : fs->n_fatent * 3 / 2 + (fs->n_fatent & 1);
		}
		if (fs->fsize < (szbfat + (SS(fs) - 1)) / SS(fs)) return FR_NO_FILESYSTEM;	/* (BPB_FATSz must not be less than the size needed) */

#if !FF_FS_READONLY
		/* Get FSInfo if available */
		fs->last_clst = fs->free_clst = 0xFFFFFFFF;		/* Initialize cluster allocation information */
		fs->fsi_flag = 0x80;
#if (FF_FS_NOFSINFO & 3) != 3
		if (fmt == FS_FAT32				/* Allow to update FSInfo only if BPB_FSInfo32 == 1 */
			&& ld_word(fs->win + BPB_FSInfo32) == 1
			&& move_window(fs, bsect + 1) == FR_OK)
		{
			fs->fsi_flag = 0;
			if (ld_word(fs->win + BS_55AA) == 0xAA55	/* Load FSInfo data if available */
				&& ld_dword(fs->win + FSI_LeadSig) == 0x41615252
				&& ld_dword(fs->win + FSI_StrucSig) == 0x61417272)
			{
#if (FF_FS_NOFSINFO & 1) == 0
				fs->free_clst = ld_dword(fs->win + FSI_Free_Count);
#endif
#if (FF_FS_NOFSINFO & 2) == 0
				fs->last_clst = ld_dword(fs->win + FSI_Nxt_Free);
#endif
			}
		}
#endif	/* (FF_FS_NOFSINFO & 3) != 3 */
#endif	/* !FF_FS_READONLY */
	}

	fs->fs_type = (BYTE)fmt;/* FAT sub-type (the filesystem object gets valid) */
	fs->id = ++Fsid;		/* Volume mount ID */
#if FF_USE_LFN == 1
	fs->lfnbuf = LfnBuf;	/* Static LFN working buffer */
#if FF_FS_EXFAT
	fs->dirbuf = DirBuf;	/* Static directory block scratchpad buuffer */
#endif
#endif
#if FF_FS_RPATH != 0
	fs->cdir = 0;			/* Initialize current directory */
#endif
#if FF_FS_LOCK				/* Clear file lock semaphores */
	clear_share(fs);
#endif
	return FR_OK;
}