fs/fat/fatent.c

Source file repositories/reference/linux-study-clean/fs/fat/fatent.c

File Facts

System
Linux kernel
Corpus path
fs/fat/fatent.c
Extension
.c
Size
21287 bytes
Lines
854
Domain
Core OS
Bucket
VFS And Filesystem Core
Inferred role
Core OS: exported/initcall integration point
Status
integration implementation candidate

Why This File Exists

Core operating-system implementation surface: boot, tasks, memory, VFS, syscall-facing interfaces, synchronization, credentials, and isolation.

Dependency Surface

Detected Declarations

Annotated Snippet

struct fatent_operations {
	void (*ent_blocknr)(struct super_block *, int, int *, sector_t *);
	void (*ent_set_ptr)(struct fat_entry *, int);
	int (*ent_bread)(struct super_block *, struct fat_entry *,
			 int, sector_t);
	int (*ent_get)(struct fat_entry *);
	void (*ent_put)(struct fat_entry *, int);
	int (*ent_next)(struct fat_entry *);
};

static DEFINE_SPINLOCK(fat12_entry_lock);

static void fat12_ent_blocknr(struct super_block *sb, int entry,
			      int *offset, sector_t *blocknr)
{
	struct msdos_sb_info *sbi = MSDOS_SB(sb);
	int bytes = entry + (entry >> 1);
	WARN_ON(!fat_valid_entry(sbi, entry));
	*offset = bytes & (sb->s_blocksize - 1);
	*blocknr = sbi->fat_start + (bytes >> sb->s_blocksize_bits);
}

static void fat_ent_blocknr(struct super_block *sb, int entry,
			    int *offset, sector_t *blocknr)
{
	struct msdos_sb_info *sbi = MSDOS_SB(sb);
	int bytes = (entry << sbi->fatent_shift);
	WARN_ON(!fat_valid_entry(sbi, entry));
	*offset = bytes & (sb->s_blocksize - 1);
	*blocknr = sbi->fat_start + (bytes >> sb->s_blocksize_bits);
}

static void fat12_ent_set_ptr(struct fat_entry *fatent, int offset)
{
	struct buffer_head **bhs = fatent->bhs;
	if (fatent->nr_bhs == 1) {
		WARN_ON(offset >= (bhs[0]->b_size - 1));
		fatent->u.ent12_p[0] = bhs[0]->b_data + offset;
		fatent->u.ent12_p[1] = bhs[0]->b_data + (offset + 1);
	} else {
		WARN_ON(offset != (bhs[0]->b_size - 1));
		fatent->u.ent12_p[0] = bhs[0]->b_data + offset;
		fatent->u.ent12_p[1] = bhs[1]->b_data;
	}
}

static void fat16_ent_set_ptr(struct fat_entry *fatent, int offset)
{
	WARN_ON(offset & (2 - 1));
	fatent->u.ent16_p = (__le16 *)(fatent->bhs[0]->b_data + offset);
}

static void fat32_ent_set_ptr(struct fat_entry *fatent, int offset)
{
	WARN_ON(offset & (4 - 1));
	fatent->u.ent32_p = (__le32 *)(fatent->bhs[0]->b_data + offset);
}

static int fat12_ent_bread(struct super_block *sb, struct fat_entry *fatent,
			   int offset, sector_t blocknr)
{
	struct buffer_head **bhs = fatent->bhs;

	WARN_ON(blocknr < MSDOS_SB(sb)->fat_start);
	fatent->fat_inode = MSDOS_SB(sb)->fat_inode;

	bhs[0] = sb_bread(sb, blocknr);
	if (!bhs[0])
		goto err;

	if ((offset + 1) < sb->s_blocksize)
		fatent->nr_bhs = 1;
	else {
		/* This entry is block boundary, it needs the next block */
		blocknr++;
		bhs[1] = sb_bread(sb, blocknr);
		if (!bhs[1])
			goto err_brelse;
		fatent->nr_bhs = 2;
	}
	fat12_ent_set_ptr(fatent, offset);
	return 0;

err_brelse:
	brelse(bhs[0]);
err:
	fat_msg_ratelimit(sb, KERN_ERR, "FAT read failed (blocknr %llu)",
			  (llu)blocknr);
	return -EIO;
}

Annotation

Implementation Notes