misc.c

LINUX1.0内核源代码,学习LINUX编程的一定要看。

/*
 *  linux/fs/msdos/misc.c
 *
 *  Written 1992,1993 by Werner Almesberger
 */

#include <linux/fs.h>
#include <linux/msdos_fs.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/stat.h>

/* Well-known binary file extensions */

static char bin_extensions[] =
  "EXECOMBINAPPSYSDRVOVLOVROBJLIBDLLPIF"	/* program code */
  "ARCZIPLHALZHZOOTARZ  ARJ"	/* common archivers */
  "TZ TAZTZPTPZ"		/* abbreviations of tar.Z and tar.zip */
  "GIFBMPTIFGL JPGPCX"		/* graphics */
  "TFMVF GF PK PXLDVI";		/* TeX */


/*
 * fs_panic reports a severe file system problem and sets the file system
 * read-only. The file system can be made writable again by remounting it.
 */

void fs_panic(struct super_block *s,char *msg)
{
	int not_ro;

	not_ro = !(s->s_flags & MS_RDONLY);
	if (not_ro) s->s_flags |= MS_RDONLY;
	printk("Filesystem panic (dev 0x%04X, mounted on 0x%04X:%ld)\n  %s\n",
	    s->s_dev,s->s_covered->i_dev,s->s_covered->i_ino,msg);
	if (not_ro)
		printk("  File system has been set read-only\n");
}


/*
 * is_binary selects optional text conversion based on the conversion mode and
 * the extension part of the file name.
 */

int is_binary(char conversion,char *extension)
{
	char *walk;

	switch (conversion) {
		case 'b':
			return 1;
		case 't':
			return 0;
		case 'a':
			for (walk = bin_extensions; *walk; walk += 3)
				if (!strncmp(extension,walk,3)) return 1;
			return 0;
		default:
			printk("Invalid conversion mode - defaulting to "
			    "binary.\n");
			return 1;
	}
}


/* File creation lock. This is system-wide to avoid deadlocks in rename. */
/* (rename might deadlock before detecting cross-FS moves.) */

static struct wait_queue *creation_wait = NULL;
static creation_lock = 0;


void lock_creation(void)
{
	while (creation_lock) sleep_on(&creation_wait);
	creation_lock = 1;
}


void unlock_creation(void)
{
	creation_lock = 0;
	wake_up(&creation_wait);
}


void lock_fat(struct super_block *sb)
{
	while (MSDOS_SB(sb)->fat_lock) sleep_on(&MSDOS_SB(sb)->fat_wait);
	MSDOS_SB(sb)->fat_lock = 1;
}


void unlock_fat(struct super_block *sb)
{
	MSDOS_SB(sb)->fat_lock = 0;
	wake_up(&MSDOS_SB(sb)->fat_wait);
}


/*
 * msdos_add_cluster tries to allocate a new cluster and adds it to the file
 * represented by inode. The cluster is zero-initialized.
 */

int msdos_add_cluster(struct inode *inode)
{
	int count,nr,limit,last,current,sector;
	void *data;
	struct buffer_head *bh;

	if (inode->i_ino == MSDOS_ROOT_INO) return -ENOSPC;
	if (!MSDOS_SB(inode->i_sb)->free_clusters) return -ENOSPC;
	lock_fat(inode->i_sb);
	limit = MSDOS_SB(inode->i_sb)->clusters;
	nr = limit; /* to keep GCC happy */
	for (count = 0; count < limit; count++) {
		nr = ((count+MSDOS_SB(inode->i_sb)->prev_free) % limit)+2;
		if (fat_access(inode->i_sb,nr,-1) == 0) break;
	}
#ifdef DEBUG
printk("free cluster: %d\n",nr);
#endif
	MSDOS_SB(inode->i_sb)->prev_free = (count+MSDOS_SB(inode->i_sb)->
	    prev_free+1) % limit;
	if (count >= limit) {
		MSDOS_SB(inode->i_sb)->free_clusters = 0;
		unlock_fat(inode->i_sb);
		return -ENOSPC;
	}
	fat_access(inode->i_sb,nr,MSDOS_SB(inode->i_sb)->fat_bits == 12 ?
	    0xff8 : 0xfff8);
	if (MSDOS_SB(inode->i_sb)->free_clusters != -1)
		MSDOS_SB(inode->i_sb)->free_clusters--;
	unlock_fat(inode->i_sb);
#ifdef DEBUG
printk("set to %x\n",fat_access(inode->i_sb,nr,-1));
#endif
	last = 0;
	if ((current = MSDOS_I(inode)->i_start) != 0) {
		cache_lookup(inode,INT_MAX,&last,&current);
		while (current && current != -1)
			if (!(current = fat_access(inode->i_sb,
			    last = current,-1))) {
				fs_panic(inode->i_sb,"File without EOF");
				return -ENOSPC;
			}
	}
#ifdef DEBUG
printk("last = %d\n",last);
#endif
	if (last) fat_access(inode->i_sb,last,nr);
	else {
		MSDOS_I(inode)->i_start = nr;
		inode->i_dirt = 1;
	}
#ifdef DEBUG
if (last) printk("next set to %d\n",fat_access(inode->i_sb,last,-1));
#endif
	for (current = 0; current < MSDOS_SB(inode->i_sb)->cluster_size;
	    current++) {
		sector = MSDOS_SB(inode->i_sb)->data_start+(nr-2)*
		    MSDOS_SB(inode->i_sb)->cluster_size+current;
#ifdef DEBUG
printk("zeroing sector %d\n",sector);
#endif
		if (current < MSDOS_SB(inode->i_sb)->cluster_size-1 &&
		    !(sector & 1)) {
			if (!(bh = getblk(inode->i_dev,sector >> 1,
			    BLOCK_SIZE)))
				printk("getblk failed\n");
			else {
				memset(bh->b_data,0,BLOCK_SIZE);
				bh->b_uptodate = 1;
			}
			current++;
		}
		else {
			if (!(bh = msdos_sread(inode->i_dev,sector,
			    &data)))
				printk("msdos_sread failed\n");
			else memset(data,0,SECTOR_SIZE);
		}
		if (bh) {
			bh->b_dirt = 1;
			brelse(bh);
		}
	}
	inode->i_blocks += MSDOS_SB(inode->i_sb)->cluster_size;
	if (S_ISDIR(inode->i_mode)) {
		if (inode->i_size & (SECTOR_SIZE-1)) {
			fs_panic(inode->i_sb,"Odd directory size");
			inode->i_size = (inode->i_size+SECTOR_SIZE) &
			    ~(SECTOR_SIZE-1);
		}
		inode->i_size += SECTOR_SIZE*MSDOS_SB(inode->i_sb)->
		    cluster_size;
#ifdef DEBUG
printk("size is %d now (%x)\n",inode->i_size,inode);
#endif
		inode->i_dirt = 1;
	}
	return 0;
}


/* Linear day numbers of the respective 1sts in non-leap years. */

static int day_n[] = { 0,31,59,90,120,151,181,212,243,273,304,334,0,0,0,0 };
		  /* JanFebMarApr May Jun Jul Aug Sep Oct Nov Dec */


extern struct timezone sys_tz;


/* Convert a MS-DOS time/date pair to a UNIX date (seconds since 1 1 70). */

int date_dos2unix(unsigned short time,unsigned short date)
{
	int month,year,secs;

	month = ((date >> 5) & 15)-1;
	year = date >> 9;
	secs = (time & 31)*2+60*((time >> 5) & 63)+(time >> 11)*3600+86400*
	    ((date & 31)-1+day_n[month]+(year/4)+year*365-((year & 3) == 0 &&
	    month < 2 ? 1 : 0)+3653);
			/* days since 1.1.70 plus 80's leap day */
	secs += sys_tz.tz_minuteswest*60;
	return secs;
}


/* Convert linear UNIX date to a MS-DOS time/date pair. */

void date_unix2dos(int unix_date,unsigned short *time,
    unsigned short *date)
{
	int day,year,nl_day,month;

	unix_date -= sys_tz.tz_minuteswest*60;
	*time = (unix_date % 60)/2+(((unix_date/60) % 60) << 5)+
	    (((unix_date/3600) % 24) << 11);
	day = unix_date/86400-3652;
	year = day/365;
	if ((year+3)/4+365*year > day) year--;
	day -= (year+3)/4+365*year;
	if (day == 59 && !(year & 3)) {
		nl_day = day;
		month = 2;
	}
	else {
		nl_day = (year & 3) || day <= 59 ? day : day-1;
		for (month = 0; month < 12; month++)
			if (day_n[month] > nl_day) break;
	}
	*date = nl_day-day_n[month-1]+1+(month << 5)+(year << 9);
}


/* Returns the inode number of the directory entry at offset pos. If bh is
   non-NULL, it is brelse'd before. Pos is incremented. The buffer header is
   returned in bh. */

int msdos_get_entry(struct inode *dir, off_t *pos,struct buffer_head **bh,
    struct msdos_dir_entry **de)
{
	int sector,offset;
	void *data;

	while (1) {
		offset = *pos;
		if ((sector = msdos_smap(dir,offset >> SECTOR_BITS)) == -1)
			return -1;
		if (!sector)
			return -1; /* beyond EOF */
		*pos += sizeof(struct msdos_dir_entry);
		if (*bh)
			brelse(*bh);
		if (!(*bh = msdos_sread(dir->i_dev,sector,&data))) {
			printk("Directory sread (sector %d) failed\n",sector);
			continue;
		}
		*de = (struct msdos_dir_entry *) (data+(offset &
		    (SECTOR_SIZE-1)));
		return (sector << MSDOS_DPS_BITS)+((offset & (SECTOR_SIZE-1)) >>
		    MSDOS_DIR_BITS);
	}
}


/*
 * Now an ugly part: this set of directory scan routines works on clusters
 * rather than on inodes and sectors. They are necessary to locate the '..'
 * directory "inode". raw_scan_sector operates in four modes:
 *
 * name     number   ino      action
 * -------- -------- -------- -------------------------------------------------
 * non-NULL -        X        Find an entry with that name
 * NULL     non-NULL non-NULL Find an entry whose data starts at *number
 * NULL     non-NULL NULL     Count subdirectories in *number. (*)
 * NULL     NULL     non-NULL Find an empty entry
 *
 * (*) The return code should be ignored. It DOES NOT indicate success or
 *     failure. *number has to be initialized to zero.
 *
 * - = not used, X = a value is returned unless NULL
 *
 * If res_bh is non-NULL, the buffer is not deallocated but returned to the
 * caller on success. res_de is set accordingly.
 *
 * If cont is non-zero, raw_found continues with the entry after the one
 * res_bh/res_de point to.
 */


#define RSS_NAME /* search for name */ \
    done = !strncmp(data[entry].name,name,MSDOS_NAME) && \
     !(data[entry].attr & ATTR_VOLUME);

#define RSS_START /* search for start cluster */ \
    done = !IS_FREE(data[entry].name) && CF_LE_W(data[entry].start) == *number;

#define RSS_FREE /* search for free entry */ \
    { \
	done = IS_FREE(data[entry].name); \
	if (done) { \
	    inode = iget(sb,sector*MSDOS_DPS+entry); \
	    if (inode) { \
	    /* Directory slots of busy deleted files aren't available yet. */ \
		done = !MSDOS_I(inode)->i_busy; \
		iput(inode); \
	    } \
	} \
    }

#define RSS_COUNT /* count subdirectories */ \
    { \
	done = 0; \
	if (!IS_FREE(data[entry].name) && (data[entry].attr & ATTR_DIR)) \
	    (*number)++; \
    }

static int raw_scan_sector(struct super_block *sb,int sector,char *name,
    int *number,int *ino,struct buffer_head **res_bh,
    struct msdos_dir_entry **res_de)
{
	struct buffer_head *bh;
	struct msdos_dir_entry *data;
	struct inode *inode;
	int entry,start,done;

	if (!(bh = msdos_sread(sb->s_dev,sector,(void **) &data))) return -EIO;
	for (entry = 0; entry < MSDOS_DPS; entry++) {
		if (name) RSS_NAME
		else {
			if (!ino) RSS_COUNT
			else {
				if (number) RSS_START
				else RSS_FREE
			}
		}
		if (done) {
			if (ino) *ino = sector*MSDOS_DPS+entry;
			start = CF_LE_W(data[entry].start);
			if (!res_bh) brelse(bh);
			else {
				*res_bh = bh;
				*res_de = &data[entry];
			}
			return start;
		}
	}
	brelse(bh);
	return -ENOENT;
}


/*
 * raw_scan_root performs raw_scan_sector on the root directory until the
 * requested entry is found or the end of the directory is reached.
 */

static int raw_scan_root(struct super_block *sb,char *name,int *number,int *ino,
    struct buffer_head **res_bh,struct msdos_dir_entry **res_de)
{
	int count,cluster;

	for (count = 0; count < MSDOS_SB(sb)->dir_entries/MSDOS_DPS; count++) {
		if ((cluster = raw_scan_sector(sb,MSDOS_SB(sb)->dir_start+count,
		    name,number,ino,res_bh,res_de)) >= 0) return cluster;
	}
	return -ENOENT;
}


/*
 * raw_scan_nonroot performs raw_scan_sector on a non-root directory until the
 * requested entry is found or the end of the directory is reached.
 */

static int raw_scan_nonroot(struct super_block *sb,int start,char *name,
    int *number,int *ino,struct buffer_head **res_bh,struct msdos_dir_entry
    **res_de)
{
	int count,cluster;

#ifdef DEBUG
	printk("raw_scan_nonroot: start=%d\n",start);
#endif
	do {
		for (count = 0; count < MSDOS_SB(sb)->cluster_size; count++) {
			if ((cluster = raw_scan_sector(sb,(start-2)*
			    MSDOS_SB(sb)->cluster_size+MSDOS_SB(sb)->data_start+
			    count,name,number,ino,res_bh,res_de)) >= 0)
				return cluster;
		}
		if (!(start = fat_access(sb,start,-1))) {
			fs_panic(sb,"FAT error");
			break;
		}
#ifdef DEBUG
	printk("next start: %d\n",start);
#endif
	}
	while (start != -1);
	return -ENOENT;
}


/*
 * raw_scan performs raw_scan_sector on any sector.
 *
 * NOTE: raw_scan must not be used on a directory that is is the process of
 *       being created.
 */

static int raw_scan(struct super_block *sb,int start,char *name,int *number,
    int *ino,struct buffer_head **res_bh,struct msdos_dir_entry **res_de)
{
	if (start)
		return raw_scan_nonroot(sb,start,name,number,ino,res_bh,res_de);
	else return raw_scan_root(sb,name,number,ino,res_bh,res_de);
}


/*
 * msdos_parent_ino returns the inode number of the parent directory of dir.
 * File creation has to be deferred while msdos_parent_ino is running to
 * prevent renames.
 */

int msdos_parent_ino(struct inode *dir,int locked)
{
	static int zero = 0;
	int error,current,prev,nr;

	if (!S_ISDIR(dir->i_mode)) panic("Non-directory fed to m_p_i");
	if (dir->i_ino == MSDOS_ROOT_INO) return dir->i_ino;
	if (!locked) lock_creation(); /* prevent renames */
	if ((current = raw_scan(dir->i_sb,MSDOS_I(dir)->i_start,MSDOS_DOTDOT,
	    &zero,NULL,NULL,NULL)) < 0) {
		if (!locked) unlock_creation();
		return current;
	}
	if (!current) nr = MSDOS_ROOT_INO;
	else {
		if ((prev = raw_scan(dir->i_sb,current,MSDOS_DOTDOT,&zero,NULL,
		    NULL,NULL)) < 0) {
			if (!locked) unlock_creation();
			return prev;
		}
		if ((error = raw_scan(dir->i_sb,prev,NULL,&current,&nr,NULL,
		    NULL)) < 0) {
			if (!locked) unlock_creation();
			return error;
		}
	}
	if (!locked) unlock_creation();
	return nr;
}


/*
 * msdos_subdirs counts the number of sub-directories of dir. It can be run
 * on directories being created.
 */

int msdos_subdirs(struct inode *dir)
{
	int count;

	count = 0;
	if (dir->i_ino == MSDOS_ROOT_INO)
		(void) raw_scan_root(dir->i_sb,NULL,&count,NULL,NULL,NULL);
	else {
		if (!MSDOS_I(dir)->i_start) return 0; /* in mkdir */
		else (void) raw_scan_nonroot(dir->i_sb,MSDOS_I(dir)->i_start,
		    NULL,&count,NULL,NULL,NULL);
	}
	return count;
}


/*
 * Scans a directory for a given file (name points to its formatted name) or
 * for an empty directory slot (name is NULL). Returns an error code or zero.
 */

int msdos_scan(struct inode *dir,char *name,struct buffer_head **res_bh,
    struct msdos_dir_entry **res_de,int *ino)
{
	int res;

	if (name)
		res = raw_scan(dir->i_sb,MSDOS_I(dir)->i_start,name,NULL,ino,
		    res_bh,res_de);
	else res = raw_scan(dir->i_sb,MSDOS_I(dir)->i_start,NULL,NULL,ino,
		    res_bh,res_de);
	return res < 0 ? res : 0;
}