* same with xv6

[mascara-docs.git] / i386 / MIT / course / src / src.lab / fs / fs.c

#include <inc/string.h>

#include "fs.h"

// --------------------------------------------------------------
// Super block
// --------------------------------------------------------------

// Validate the file system super-block.
void
check_super(void)
{
        if (super->s_magic != FS_MAGIC)
                panic("bad file system magic number");

        if (super->s_nblocks > DISKSIZE/BLKSIZE)
                panic("file system is too large");

        cprintf("superblock is good\n");
}

// --------------------------------------------------------------
// Free block bitmap
// --------------------------------------------------------------

// Check to see if the block bitmap indicates that block 'blockno' is free.
// Return 1 if the block is free, 0 if not.
bool
block_is_free(uint32_t blockno)
{
        if (super == 0 || blockno >= super->s_nblocks)
                return 0;
        if (bitmap[blockno / 32] & (1 << (blockno % 32)))
                return 1;
        return 0;
}

// Mark a block free in the bitmap
void
free_block(uint32_t blockno)
{
        // Blockno zero is the null pointer of block numbers.
        if (blockno == 0)
                panic("attempt to free zero block");
        bitmap[blockno/32] |= 1<<(blockno%32);
}

// Search the bitmap for a free block and allocate it.  When you
// allocate a block, immediately flush the changed bitmap block
// to disk.
//
// Return block number allocated on success,
// -E_NO_DISK if we are out of blocks.
//
// Hint: use free_block as an example for manipulating the bitmap.
int
alloc_block(void)
{
        // The bitmap consists of one or more blocks.  A single bitmap block
        // contains the in-use bits for BLKBITSIZE blocks.  There are
        // super->s_nblocks blocks in the disk altogether.

        // LAB 5: Your code here.
        panic("alloc_block not implemented");
        return -E_NO_DISK;
}

// Validate the file system bitmap.
//
// Check that all reserved blocks -- 0, 1, and the bitmap blocks themselves --
// are all marked as in-use.
void
check_bitmap(void)
{
        uint32_t i;

        // Make sure all bitmap blocks are marked in-use
        for (i = 0; i * BLKBITSIZE < super->s_nblocks; i++)
                assert(!block_is_free(2+i));

        // Make sure the reserved and root blocks are marked in-use.
        assert(!block_is_free(0));
        assert(!block_is_free(1));

        cprintf("bitmap is good\n");
}

// --------------------------------------------------------------
// File system structures
// --------------------------------------------------------------

// Initialize the file system
void
fs_init(void)
{
        static_assert(sizeof(struct File) == 256);

        // Find a JOS disk.  Use the second IDE disk (number 1) if available.
        if (ide_probe_disk1())
                ide_set_disk(1);
        else
                ide_set_disk(0);

        bc_init();

        // Set "super" to point to the super block.
        super = diskaddr(1);
        // Set "bitmap" to the beginning of the first bitmap block.
        bitmap = diskaddr(2);

        check_super();
        check_bitmap();
}

// Find the disk block number slot for the 'filebno'th block in file 'f'.
// Set '*ppdiskbno' to point to that slot.
// The slot will be one of the f->f_direct[] entries,
// or an entry in the indirect block.
// When 'alloc' is set, this function will allocate an indirect block
// if necessary.
//
// Returns:
//      0 on success (but note that *ppdiskbno might equal 0).
//      -E_NOT_FOUND if the function needed to allocate an indirect block, but
//              alloc was 0.
//      -E_NO_DISK if there's no space on the disk for an indirect block.
//      -E_INVAL if filebno is out of range (it's >= NDIRECT + NINDIRECT).
//
// Analogy: This is like pgdir_walk for files.
// Hint: Don't forget to clear any block you allocate.
static int
file_block_walk(struct File *f, uint32_t filebno, uint32_t **ppdiskbno, bool alloc)
{
        // LAB 5: Your code here.
        panic("file_block_walk not implemented");
}

// Set *blk to the address in memory where the filebno'th
// block of file 'f' would be mapped.
// Allocate the block if it doesn't yet exist.
//
// Returns 0 on success, < 0 on error.  Errors are:
//      -E_NO_DISK if a block needed to be allocated but the disk is full.
//      -E_INVAL if filebno is out of range.
//
// Hint: Use file_block_walk and alloc_block.
int
file_get_block(struct File *f, uint32_t filebno, char **blk)
{
        // LAB 5: Your code here.
        panic("file_get_block not implemented");
}

// Try to find a file named "name" in dir.  If so, set *file to it.
//
// Returns 0 and sets *file on success, < 0 on error.  Errors are:
//      -E_NOT_FOUND if the file is not found
static int
dir_lookup(struct File *dir, const char *name, struct File **file)
{
        int r;
        uint32_t i, j, nblock;
        char *blk;
        struct File *f;

        // Search dir for name.
        // We maintain the invariant that the size of a directory-file
        // is always a multiple of the file system's block size.
        assert((dir->f_size % BLKSIZE) == 0);
        nblock = dir->f_size / BLKSIZE;
        for (i = 0; i < nblock; i++) {
                if ((r = file_get_block(dir, i, &blk)) < 0)
                        return r;
                f = (struct File*) blk;
                for (j = 0; j < BLKFILES; j++)
                        if (strcmp(f[j].f_name, name) == 0) {
                                *file = &f[j];
                                return 0;
                        }
        }
        return -E_NOT_FOUND;
}

// Set *file to point at a free File structure in dir.  The caller is
// responsible for filling in the File fields.
static int
dir_alloc_file(struct File *dir, struct File **file)
{
        int r;
        uint32_t nblock, i, j;
        char *blk;
        struct File *f;

        assert((dir->f_size % BLKSIZE) == 0);
        nblock = dir->f_size / BLKSIZE;
        for (i = 0; i < nblock; i++) {
                if ((r = file_get_block(dir, i, &blk)) < 0)
                        return r;
                f = (struct File*) blk;
                for (j = 0; j < BLKFILES; j++)
                        if (f[j].f_name[0] == '\0') {
                                *file = &f[j];
                                return 0;
                        }
        }
        dir->f_size += BLKSIZE;
        if ((r = file_get_block(dir, i, &blk)) < 0)
                return r;
        f = (struct File*) blk;
        *file = &f[0];
        return 0;
}

// Skip over slashes.
static const char*
skip_slash(const char *p)
{
        while (*p == '/')
                p++;
        return p;
}

// Evaluate a path name, starting at the root.
// On success, set *pf to the file we found
// and set *pdir to the directory the file is in.
// If we cannot find the file but find the directory
// it should be in, set *pdir and copy the final path
// element into lastelem.
static int
walk_path(const char *path, struct File **pdir, struct File **pf, char *lastelem)
{
        const char *p;
        char name[MAXNAMELEN];
        struct File *dir, *f;
        int r;

        // if (*path != '/')
        //      return -E_BAD_PATH;
        path = skip_slash(path);
        f = &super->s_root;
        dir = 0;
        name[0] = 0;

        if (pdir)
                *pdir = 0;
        *pf = 0;
        while (*path != '\0') {
                dir = f;
                p = path;
                while (*path != '/' && *path != '\0')
                        path++;
                if (path - p >= MAXNAMELEN)
                        return -E_BAD_PATH;
                memmove(name, p, path - p);
                name[path - p] = '\0';
                path = skip_slash(path);

                if (dir->f_type != FTYPE_DIR)
                        return -E_NOT_FOUND;

                if ((r = dir_lookup(dir, name, &f)) < 0) {
                        if (r == -E_NOT_FOUND && *path == '\0') {
                                if (pdir)
                                        *pdir = dir;
                                if (lastelem)
                                        strcpy(lastelem, name);
                                *pf = 0;
                        }
                        return r;
                }
        }

        if (pdir)
                *pdir = dir;
        *pf = f;
        return 0;
}

// --------------------------------------------------------------
// File operations
// --------------------------------------------------------------

// Create "path".  On success set *pf to point at the file and return 0.
// On error return < 0.
int
file_create(const char *path, struct File **pf)
{
        char name[MAXNAMELEN];
        int r;
        struct File *dir, *f;

        if ((r = walk_path(path, &dir, &f, name)) == 0)
                return -E_FILE_EXISTS;
        if (r != -E_NOT_FOUND || dir == 0)
                return r;
        if ((r = dir_alloc_file(dir, &f)) < 0)
                return r;
        strcpy(f->f_name, name);
        *pf = f;
        file_flush(dir);
        return 0;
}

// Open "path".  On success set *pf to point at the file and return 0.
// On error return < 0.
int
file_open(const char *path, struct File **pf)
{
        return walk_path(path, 0, pf, 0);
}

// Read count bytes from f into buf, starting from seek position
// offset.  This meant to mimic the standard pread function.
// Returns the number of bytes read, < 0 on error.
ssize_t
file_read(struct File *f, void *buf, size_t count, off_t offset)
{
        int r, bn;
        off_t pos;
        char *blk;

        if (offset >= f->f_size)
                return 0;

        count = MIN(count, f->f_size - offset);

        for (pos = offset; pos < offset + count; ) {
                if ((r = file_get_block(f, pos / BLKSIZE, &blk)) < 0)
                        return r;
                bn = MIN(BLKSIZE - pos % BLKSIZE, offset + count - pos);
                memmove(buf, blk + pos % BLKSIZE, bn);
                pos += bn;
                buf += bn;
        }

        return count;
}

// Write count bytes from buf into f, starting at seek position
// offset.  This is meant to mimic the standard pwrite function.
// Extends the file if necessary.
// Returns the number of bytes written, < 0 on error.
int
file_write(struct File *f, const void *buf, size_t count, off_t offset)
{
        int r, bn;
        off_t pos;
        char *blk;

        // Extend file if necessary
        if (offset + count > f->f_size)
                if ((r = file_set_size(f, offset + count)) < 0)
                        return r;

        for (pos = offset; pos < offset + count; ) {
                if ((r = file_get_block(f, pos / BLKSIZE, &blk)) < 0)
                        return r;
                bn = MIN(BLKSIZE - pos % BLKSIZE, offset + count - pos);
                memmove(blk + pos % BLKSIZE, buf, bn);
                pos += bn;
                buf += bn;
        }

        return count;
}

// Remove a block from file f.  If it's not there, just silently succeed.
// Returns 0 on success, < 0 on error.
static int
file_free_block(struct File *f, uint32_t filebno)
{
        int r;
        uint32_t *ptr;

        if ((r = file_block_walk(f, filebno, &ptr, 0)) < 0)
                return r;
        if (*ptr) {
                free_block(*ptr);
                *ptr = 0;
        }
        return 0;
}

// Remove any blocks currently used by file 'f',
// but not necessary for a file of size 'newsize'.
// For both the old and new sizes, figure out the number of blocks required,
// and then clear the blocks from new_nblocks to old_nblocks.
// If the new_nblocks is no more than NDIRECT, and the indirect block has
// been allocated (f->f_indirect != 0), then free the indirect block too.
// (Remember to clear the f->f_indirect pointer so you'll know
// whether it's valid!)
// Do not change f->f_size.
static void
file_truncate_blocks(struct File *f, off_t newsize)
{
        int r;
        uint32_t bno, old_nblocks, new_nblocks;

        old_nblocks = (f->f_size + BLKSIZE - 1) / BLKSIZE;
        new_nblocks = (newsize + BLKSIZE - 1) / BLKSIZE;
        for (bno = new_nblocks; bno < old_nblocks; bno++)
                if ((r = file_free_block(f, bno)) < 0)
                        cprintf("warning: file_free_block: %e", r);

        if (new_nblocks <= NDIRECT && f->f_indirect) {
                free_block(f->f_indirect);
                f->f_indirect = 0;
        }
}

// Set the size of file f, truncating or extending as necessary.
int
file_set_size(struct File *f, off_t newsize)
{
        if (f->f_size > newsize)
                file_truncate_blocks(f, newsize);
        f->f_size = newsize;
        flush_block(f);
        return 0;
}

// Flush the contents and metadata of file f out to disk.
// Loop over all the blocks in file.
// Translate the file block number into a disk block number
// and then check whether that disk block is dirty.  If so, write it out.
void
file_flush(struct File *f)
{
        int i;
        uint32_t *pdiskbno;

        for (i = 0; i < (f->f_size + BLKSIZE - 1) / BLKSIZE; i++) {
                if (file_block_walk(f, i, &pdiskbno, 0) < 0 ||
                    pdiskbno == NULL || *pdiskbno == 0)
                        continue;
                flush_block(diskaddr(*pdiskbno));
        }
        flush_block(f);
        if (f->f_indirect)
                flush_block(diskaddr(f->f_indirect));
}

// Remove a file by truncating it and then zeroing the name.
int
file_remove(const char *path)
{
        int r;
        struct File *f;

        if ((r = walk_path(path, 0, &f, 0)) < 0)
                return r;

        file_truncate_blocks(f, 0);
        f->f_name[0] = '\0';
        f->f_size = 0;
        flush_block(f);

        return 0;
}

// Sync the entire file system.  A big hammer.
void
fs_sync(void)
{
        int i;
        for (i = 1; i < super->s_nblocks; i++)
                flush_block(diskaddr(i));
}