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minix/servers/mfs/read.c

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#include "fs.h"
#include <stddef.h>
#include <string.h>
#include <stdlib.h>
#include <minix/com.h>
#include <minix/u64.h>
#include "buf.h"
#include "inode.h"
#include "super.h"
#include <minix/vfsif.h>
#include <assert.h>
FORWARD _PROTOTYPE( struct buf *rahead, (struct inode *rip, block_t baseblock,
u64_t position, unsigned bytes_ahead) );
FORWARD _PROTOTYPE( int rw_chunk, (struct inode *rip, u64_t position,
unsigned off, size_t chunk, unsigned left, int rw_flag,
cp_grant_id_t gid, unsigned buf_off, unsigned int block_size,
int *completed) );
PRIVATE char getdents_buf[GETDENTS_BUFSIZ];
/*===========================================================================*
* fs_readwrite *
*===========================================================================*/
PUBLIC int fs_readwrite(void)
{
int r, rw_flag, block_spec;
int regular;
cp_grant_id_t gid;
off_t position, f_size, bytes_left;
unsigned int off, cum_io, block_size, chunk;
mode_t mode_word;
int completed;
struct inode *rip;
size_t nrbytes;
r = OK;
/* Find the inode referred */
if ((rip = find_inode(fs_dev, (ino_t) fs_m_in.REQ_INODE_NR)) == NULL)
return(EINVAL);
mode_word = rip->i_mode & I_TYPE;
regular = (mode_word == I_REGULAR || mode_word == I_NAMED_PIPE);
block_spec = (mode_word == I_BLOCK_SPECIAL ? 1 : 0);
/* Determine blocksize */
if (block_spec) {
block_size = get_block_size( (dev_t) rip->i_zone[0]);
f_size = MAX_FILE_POS;
} else {
block_size = rip->i_sp->s_block_size;
f_size = rip->i_size;
}
/* Get the values from the request message */
rw_flag = (fs_m_in.m_type == REQ_READ ? READING : WRITING);
gid = (cp_grant_id_t) fs_m_in.REQ_GRANT;
position = (off_t) fs_m_in.REQ_SEEK_POS_LO;
nrbytes = (size_t) fs_m_in.REQ_NBYTES;
rdwt_err = OK; /* set to EIO if disk error occurs */
/* If this is file i/o, check we can write */
if (rw_flag == WRITING && !block_spec) {
if(rip->i_sp->s_rd_only)
return EROFS;
/* Check in advance to see if file will grow too big. */
if (position > (off_t) (rip->i_sp->s_max_size - nrbytes))
return(EFBIG);
/* Clear the zone containing present EOF if hole about
* to be created. This is necessary because all unwritten
* blocks prior to the EOF must read as zeros.
*/
if(position > f_size) clear_zone(rip, f_size, 0);
}
/* If this is block i/o, check we can write */
if(block_spec && rw_flag == WRITING &&
(dev_t) rip->i_zone[0] == superblock.s_dev && superblock.s_rd_only)
return EROFS;
cum_io = 0;
/* Split the transfer into chunks that don't span two blocks. */
while (nrbytes > 0) {
off = ((unsigned int) position) % block_size; /* offset in blk*/
chunk = min(nrbytes, block_size - off);
if (rw_flag == READING) {
bytes_left = f_size - position;
if (position >= f_size) break; /* we are beyond EOF */
if (chunk > (unsigned int) bytes_left) chunk = bytes_left;
}
/* Read or write 'chunk' bytes. */
r = rw_chunk(rip, cvul64((unsigned long) position), off, chunk,
nrbytes, rw_flag, gid, cum_io, block_size, &completed);
if (r != OK) break; /* EOF reached */
if (rdwt_err < 0) break;
/* Update counters and pointers. */
nrbytes -= chunk; /* bytes yet to be read */
cum_io += chunk; /* bytes read so far */
position += (off_t) chunk; /* position within the file */
}
fs_m_out.RES_SEEK_POS_LO = position; /* It might change later and the VFS
has to know this value */
/* On write, update file size and access time. */
if (rw_flag == WRITING) {
if (regular || mode_word == I_DIRECTORY) {
if (position > f_size) rip->i_size = position;
}
}
rip->i_seek = NO_SEEK;
if (rdwt_err != OK) r = rdwt_err; /* check for disk error */
if (rdwt_err == END_OF_FILE) r = OK;
/* even on a ROFS, writing to a device node on it is fine,
* just don't update the inode stats for it. And dito for reading.
*/
if (r == OK && !rip->i_sp->s_rd_only) {
if (rw_flag == READING) rip->i_update |= ATIME;
if (rw_flag == WRITING) rip->i_update |= CTIME | MTIME;
IN_MARKDIRTY(rip); /* inode is thus now dirty */
}
fs_m_out.RES_NBYTES = cum_io;
return(r);
}
/*===========================================================================*
* fs_breadwrite *
*===========================================================================*/
PUBLIC int fs_breadwrite(void)
{
int r, rw_flag, completed;
cp_grant_id_t gid;
u64_t position;
unsigned int off, cum_io, chunk, block_size;
size_t nrbytes;
dev_t target_dev;
/* Pseudo inode for rw_chunk */
struct inode rip;
r = OK;
target_dev = (dev_t) fs_m_in.REQ_DEV2;
/* Get the values from the request message */
rw_flag = (fs_m_in.m_type == REQ_BREAD ? READING : WRITING);
gid = (cp_grant_id_t) fs_m_in.REQ_GRANT;
position = make64((unsigned long) fs_m_in.REQ_SEEK_POS_LO,
(unsigned long) fs_m_in.REQ_SEEK_POS_HI);
nrbytes = (size_t) fs_m_in.REQ_NBYTES;
block_size = get_block_size(target_dev);
/* Don't block-write to a RO-mounted filesystem. */
if(superblock.s_dev == target_dev && superblock.s_rd_only)
return EROFS;
rip.i_zone[0] = (zone_t) target_dev;
rip.i_mode = I_BLOCK_SPECIAL;
rip.i_size = 0;
rdwt_err = OK; /* set to EIO if disk error occurs */
cum_io = 0;
/* Split the transfer into chunks that don't span two blocks. */
while (nrbytes > 0) {
off = rem64u(position, block_size); /* offset in blk*/
chunk = min(nrbytes, block_size - off);
/* Read or write 'chunk' bytes. */
r = rw_chunk(&rip, position, off, chunk, nrbytes, rw_flag, gid,
cum_io, block_size, &completed);
if (r != OK) break; /* EOF reached */
if (rdwt_err < 0) break;
/* Update counters and pointers. */
nrbytes -= chunk; /* bytes yet to be read */
cum_io += chunk; /* bytes read so far */
position = add64ul(position, chunk); /* position within the file */
}
fs_m_out.RES_SEEK_POS_LO = ex64lo(position);
fs_m_out.RES_SEEK_POS_HI = ex64hi(position);
if (rdwt_err != OK) r = rdwt_err; /* check for disk error */
if (rdwt_err == END_OF_FILE) r = OK;
fs_m_out.RES_NBYTES = cum_io;
return(r);
}
/*===========================================================================*
* rw_chunk *
*===========================================================================*/
PRIVATE int rw_chunk(rip, position, off, chunk, left, rw_flag, gid,
buf_off, block_size, completed)
register struct inode *rip; /* pointer to inode for file to be rd/wr */
u64_t position; /* position within file to read or write */
unsigned off; /* off within the current block */
unsigned int chunk; /* number of bytes to read or write */
unsigned left; /* max number of bytes wanted after position */
int rw_flag; /* READING or WRITING */
cp_grant_id_t gid; /* grant */
unsigned buf_off; /* offset in grant */
unsigned int block_size; /* block size of FS operating on */
int *completed; /* number of bytes copied */
{
/* Read or write (part of) a block. */
register struct buf *bp;
register int r = OK;
int n, block_spec;
block_t b;
dev_t dev;
*completed = 0;
block_spec = (rip->i_mode & I_TYPE) == I_BLOCK_SPECIAL;
if (block_spec) {
b = div64u(position, block_size);
dev = (dev_t) rip->i_zone[0];
} else {
if (ex64hi(position) != 0)
panic("rw_chunk: position too high");
b = read_map(rip, (off_t) ex64lo(position));
dev = rip->i_dev;
}
if (!block_spec && b == NO_BLOCK) {
if (rw_flag == READING) {
/* Reading from a nonexistent block. Must read as all zeros.*/
bp = get_block(NO_DEV, NO_BLOCK, NORMAL); /* get a buffer */
zero_block(bp);
} else {
/* Writing to a nonexistent block. Create and enter in inode.*/
if ((bp = new_block(rip, (off_t) ex64lo(position))) == NULL)
return(err_code);
}
} else if (rw_flag == READING) {
/* Read and read ahead if convenient. */
bp = rahead(rip, b, position, left);
} else {
/* Normally an existing block to be partially overwritten is first read
* in. However, a full block need not be read in. If it is already in
* the cache, acquire it, otherwise just acquire a free buffer.
*/
n = (chunk == block_size ? NO_READ : NORMAL);
if (!block_spec && off == 0 && (off_t) ex64lo(position) >= rip->i_size)
n = NO_READ;
bp = get_block(dev, b, n);
}
/* In all cases, bp now points to a valid buffer. */
if (bp == NULL)
panic("bp not valid in rw_chunk; this can't happen");
if (rw_flag == WRITING && chunk != block_size && !block_spec &&
(off_t) ex64lo(position) >= rip->i_size && off == 0) {
zero_block(bp);
}
if (rw_flag == READING) {
/* Copy a chunk from the block buffer to user space. */
r = sys_safecopyto(VFS_PROC_NR, gid, (vir_bytes) buf_off,
(vir_bytes) (bp->b_data+off), (size_t) chunk, D);
} else if(!block_write_ok(bp)) {
/* Let cache layer veto writing to this block */
printf("MFS: block write not allowed\n");
r = EPERM;
} else {
/* Copy a chunk from user space to the block buffer. */
r = sys_safecopyfrom(VFS_PROC_NR, gid, (vir_bytes) buf_off,
(vir_bytes) (bp->b_data+off), (size_t) chunk, D);
MARKDIRTY(bp);
}
n = (off + chunk == block_size ? FULL_DATA_BLOCK : PARTIAL_DATA_BLOCK);
put_block(bp, n);
return(r);
}
/*===========================================================================*
* read_map *
*===========================================================================*/
PUBLIC block_t read_map(rip, position)
register struct inode *rip; /* ptr to inode to map from */
off_t position; /* position in file whose blk wanted */
{
/* Given an inode and a position within the corresponding file, locate the
* block (not zone) number in which that position is to be found and return it.
*/
struct buf *bp;
zone_t z;
int scale, boff, index, zind;
unsigned int dzones, nr_indirects;
block_t b;
unsigned long excess, zone, block_pos;
scale = rip->i_sp->s_log_zone_size; /* for block-zone conversion */
block_pos = position/rip->i_sp->s_block_size; /* relative blk # in file */
zone = block_pos >> scale; /* position's zone */
boff = (int) (block_pos - (zone << scale) ); /* relative blk # within zone */
dzones = rip->i_ndzones;
nr_indirects = rip->i_nindirs;
/* Is 'position' to be found in the inode itself? */
if (zone < dzones) {
zind = (int) zone; /* index should be an int */
z = rip->i_zone[zind];
if (z == NO_ZONE) return(NO_BLOCK);
b = (block_t) ((z << scale) + boff);
return(b);
}
/* It is not in the inode, so it must be single or double indirect. */
excess = zone - dzones; /* first Vx_NR_DZONES don't count */
if (excess < nr_indirects) {
/* 'position' can be located via the single indirect block. */
z = rip->i_zone[dzones];
} else {
/* 'position' can be located via the double indirect block. */
if ( (z = rip->i_zone[dzones+1]) == NO_ZONE) return(NO_BLOCK);
excess -= nr_indirects; /* single indir doesn't count*/
b = (block_t) z << scale;
ASSERT(rip->i_dev != NO_DEV);
index = (int) (excess/nr_indirects);
if ((unsigned int) index > rip->i_nindirs)
return(NO_BLOCK); /* Can't go beyond double indirects */
bp = get_block(rip->i_dev, b, NORMAL); /* get double indirect block */
ASSERT(bp->b_dev != NO_DEV);
ASSERT(bp->b_dev == rip->i_dev);
z = rd_indir(bp, index); /* z= zone for single*/
put_block(bp, INDIRECT_BLOCK); /* release double ind block */
excess = excess % nr_indirects; /* index into single ind blk */
}
/* 'z' is zone num for single indirect block; 'excess' is index into it. */
if (z == NO_ZONE) return(NO_BLOCK);
b = (block_t) z << scale; /* b is blk # for single ind */
bp = get_block(rip->i_dev, b, NORMAL); /* get single indirect block */
z = rd_indir(bp, (int) excess); /* get block pointed to */
put_block(bp, INDIRECT_BLOCK); /* release single indir blk */
if (z == NO_ZONE) return(NO_BLOCK);
b = (block_t) ((z << scale) + boff);
return(b);
}
/*===========================================================================*
* rd_indir *
*===========================================================================*/
PUBLIC zone_t rd_indir(bp, index)
struct buf *bp; /* pointer to indirect block */
int index; /* index into *bp */
{
/* Given a pointer to an indirect block, read one entry. The reason for
* making a separate routine out of this is that there are four cases:
* V1 (IBM and 68000), and V2 (IBM and 68000).
*/
struct super_block *sp;
zone_t zone; /* V2 zones are longs (shorts in V1) */
if(bp == NULL)
panic("rd_indir() on NULL");
sp = get_super(bp->b_dev); /* need super block to find file sys type */
/* read a zone from an indirect block */
if (sp->s_version == V1)
zone = (zone_t) conv2(sp->s_native, (int) bp->b_v1_ind[index]);
else
zone = (zone_t) conv4(sp->s_native, (long) bp->b_v2_ind[index]);
if (zone != NO_ZONE &&
(zone < (zone_t) sp->s_firstdatazone || zone >= sp->s_zones)) {
printf("Illegal zone number %ld in indirect block, index %d\n",
(long) zone, index);
panic("check file system");
}
return(zone);
}
/*===========================================================================*
* rahead *
*===========================================================================*/
PRIVATE struct buf *rahead(rip, baseblock, position, bytes_ahead)
register struct inode *rip; /* pointer to inode for file to be read */
block_t baseblock; /* block at current position */
u64_t position; /* position within file */
unsigned bytes_ahead; /* bytes beyond position for immediate use */
{
/* Fetch a block from the cache or the device. If a physical read is
* required, prefetch as many more blocks as convenient into the cache.
* This usually covers bytes_ahead and is at least BLOCKS_MINIMUM.
* The device driver may decide it knows better and stop reading at a
* cylinder boundary (or after an error). Rw_scattered() puts an optional
* flag on all reads to allow this.
*/
/* Minimum number of blocks to prefetch. */
# define BLOCKS_MINIMUM (nr_bufs < 50 ? 18 : 32)
int block_spec, scale, read_q_size;
unsigned int blocks_ahead, fragment, block_size;
block_t block, blocks_left;
off_t ind1_pos;
dev_t dev;
struct buf *bp;
static unsigned int readqsize = 0;
static struct buf **read_q;
if(readqsize != nr_bufs) {
if(readqsize > 0) {
assert(read_q != NULL);
free(read_q);
}
if(!(read_q = malloc(sizeof(read_q[0])*nr_bufs)))
panic("couldn't allocate read_q");
readqsize = nr_bufs;
}
block_spec = (rip->i_mode & I_TYPE) == I_BLOCK_SPECIAL;
if (block_spec)
dev = (dev_t) rip->i_zone[0];
else
dev = rip->i_dev;
block_size = get_block_size(dev);
block = baseblock;
bp = get_block(dev, block, PREFETCH);
assert(bp != NULL);
if (bp->b_dev != NO_DEV) return(bp);
/* The best guess for the number of blocks to prefetch: A lot.
* It is impossible to tell what the device looks like, so we don't even
* try to guess the geometry, but leave it to the driver.
*
* The floppy driver can read a full track with no rotational delay, and it
* avoids reading partial tracks if it can, so handing it enough buffers to
* read two tracks is perfect. (Two, because some diskette types have
* an odd number of sectors per track, so a block may span tracks.)
*
* The disk drivers don't try to be smart. With todays disks it is
* impossible to tell what the real geometry looks like, so it is best to
* read as much as you can. With luck the caching on the drive allows
* for a little time to start the next read.
*
* The current solution below is a bit of a hack, it just reads blocks from
* the current file position hoping that more of the file can be found. A
* better solution must look at the already available zone pointers and
* indirect blocks (but don't call read_map!).
*/
fragment = rem64u(position, block_size);
position = sub64u(position, fragment);
bytes_ahead += fragment;
blocks_ahead = (bytes_ahead + block_size - 1) / block_size;
if (block_spec && rip->i_size == 0) {
blocks_left = (block_t) NR_IOREQS;
} else {
blocks_left = (block_t) (rip->i_size-ex64lo(position)+(block_size-1)) /
block_size;
/* Go for the first indirect block if we are in its neighborhood. */
if (!block_spec) {
scale = rip->i_sp->s_log_zone_size;
ind1_pos = (off_t) rip->i_ndzones * (block_size << scale);
if ((off_t) ex64lo(position) <= ind1_pos &&
rip->i_size > ind1_pos) {
blocks_ahead++;
blocks_left++;
}
}
}
/* No more than the maximum request. */
if (blocks_ahead > NR_IOREQS) blocks_ahead = NR_IOREQS;
/* Read at least the minimum number of blocks, but not after a seek. */
if (blocks_ahead < BLOCKS_MINIMUM && rip->i_seek == NO_SEEK)
blocks_ahead = BLOCKS_MINIMUM;
/* Can't go past end of file. */
if (blocks_ahead > blocks_left) blocks_ahead = blocks_left;
read_q_size = 0;
/* Acquire block buffers. */
for (;;) {
read_q[read_q_size++] = bp;
if (--blocks_ahead == 0) break;
/* Don't trash the cache, leave 4 free. */
if (bufs_in_use >= nr_bufs - 4) break;
block++;
bp = get_block(dev, block, PREFETCH);
if (bp->b_dev != NO_DEV) {
/* Oops, block already in the cache, get out. */
put_block(bp, FULL_DATA_BLOCK);
break;
}
}
rw_scattered(dev, read_q, read_q_size, READING);
return(get_block(dev, baseblock, NORMAL));
}
/*===========================================================================*
* fs_getdents *
*===========================================================================*/
PUBLIC int fs_getdents(void)
{
register struct inode *rip;
int o, r, done;
unsigned int block_size, len, reclen;
ino_t ino;
block_t b;
cp_grant_id_t gid;
size_t size, tmpbuf_off, userbuf_off;
off_t pos, off, block_pos, new_pos, ent_pos;
struct buf *bp;
struct direct *dp;
struct dirent *dep;
char *cp;
ino = (ino_t) fs_m_in.REQ_INODE_NR;
gid = (gid_t) fs_m_in.REQ_GRANT;
size = (size_t) fs_m_in.REQ_MEM_SIZE;
pos = (off_t) fs_m_in.REQ_SEEK_POS_LO;
/* Check whether the position is properly aligned */
if( (unsigned int) pos % DIR_ENTRY_SIZE)
return(ENOENT);
if( (rip = get_inode(fs_dev, ino)) == NULL)
return(EINVAL);
block_size = rip->i_sp->s_block_size;
off = (pos % block_size); /* Offset in block */
block_pos = pos - off;
done = FALSE; /* Stop processing directory blocks when done is set */
tmpbuf_off = 0; /* Offset in getdents_buf */
memset(getdents_buf, '\0', GETDENTS_BUFSIZ); /* Avoid leaking any data */
userbuf_off = 0; /* Offset in the user's buffer */
/* The default position for the next request is EOF. If the user's buffer
* fills up before EOF, new_pos will be modified. */
new_pos = rip->i_size;
for(; block_pos < rip->i_size; block_pos += block_size) {
b = read_map(rip, block_pos); /* get block number */
/* Since directories don't have holes, 'b' cannot be NO_BLOCK. */
bp = get_block(rip->i_dev, b, NORMAL); /* get a dir block */
assert(bp != NULL);
/* Search a directory block. */
if (block_pos < pos)
dp = &bp->b_dir[off / DIR_ENTRY_SIZE];
else
dp = &bp->b_dir[0];
for (; dp < &bp->b_dir[NR_DIR_ENTRIES(block_size)]; dp++) {
if (dp->mfs_d_ino == 0)
continue; /* Entry is not in use */
/* Compute the length of the name */
cp = memchr(dp->mfs_d_name, '\0', sizeof(dp->mfs_d_name));
if (cp == NULL)
len = sizeof(dp->mfs_d_name);
else
len = cp - (dp->mfs_d_name);
/* Compute record length */
reclen = offsetof(struct dirent, d_name) + len + 1;
o = (reclen % sizeof(long));
if (o != 0)
reclen += sizeof(long) - o;
/* Need the position of this entry in the directory */
ent_pos = block_pos + ((char *) dp - (bp->b_data));
if(tmpbuf_off + reclen > GETDENTS_BUFSIZ) {
r = sys_safecopyto(VFS_PROC_NR, gid,
(vir_bytes) userbuf_off,
(vir_bytes) getdents_buf,
(size_t) tmpbuf_off, D);
if (r != OK) {
put_inode(rip);
return(r);
}
userbuf_off += tmpbuf_off;
tmpbuf_off = 0;
}
if(userbuf_off + tmpbuf_off + reclen > size) {
/* The user has no space for one more record */
done = TRUE;
/* Record the position of this entry, it is the
* starting point of the next request (unless the
* postion is modified with lseek).
*/
new_pos = ent_pos;
break;
}
dep = (struct dirent *) &getdents_buf[tmpbuf_off];
dep->d_ino = dp->mfs_d_ino;
dep->d_off = ent_pos;
dep->d_reclen = (unsigned short) reclen;
memcpy(dep->d_name, dp->mfs_d_name, len);
dep->d_name[len] = '\0';
tmpbuf_off += reclen;
}
put_block(bp, DIRECTORY_BLOCK);
if(done)
break;
}
if(tmpbuf_off != 0) {
r = sys_safecopyto(VFS_PROC_NR, gid, (vir_bytes) userbuf_off,
(vir_bytes) getdents_buf, (size_t) tmpbuf_off, D);
if (r != OK) {
put_inode(rip);
return(r);
}
userbuf_off += tmpbuf_off;
}
if(done && userbuf_off == 0)
r = EINVAL; /* The user's buffer is too small */
else {
fs_m_out.RES_NBYTES = userbuf_off;
fs_m_out.RES_SEEK_POS_LO = new_pos;
if(!rip->i_sp->s_rd_only) {
rip->i_update |= ATIME;
IN_MARKDIRTY(rip);
}
r = OK;
}
put_inode(rip); /* release the inode */
return(r);
}
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