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unix_io.c

/*
 * unix_io.c --- This is the Unix I/O interface to the I/O manager.
 *
 * Implements a one-block write-through cache.
 *
 * Copyright (C) 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001,
 *    2002 by Theodore Ts'o.
 *
 * %Begin-Header%
 * This file may be redistributed under the terms of the GNU Public
 * License.
 * %End-Header%
 */

#define _LARGEFILE_SOURCE
#define _LARGEFILE64_SOURCE

#include <stdio.h>
#include <string.h>
#if HAVE_UNISTD_H
#include <unistd.h>
#endif
#if HAVE_ERRNO_H
#include <errno.h>
#endif
#include <fcntl.h>
#include <time.h>
#if HAVE_SYS_STAT_H
#include <sys/stat.h>
#endif
#if HAVE_SYS_TYPES_H
#include <sys/types.h>
#endif
#include <sys/resource.h>

#include "ext2_fs.h"
#include "ext2fs.h"

/*
 * For checking structure magic numbers...
 */

#define EXT2_CHECK_MAGIC(struct, code) \
        if ((struct)->magic != (code)) return (code)

struct unix_cache {
      char        *buf;
      unsigned long     block;
      int         access_time;
      int         dirty:1;
      int         in_use:1;
};

#define CACHE_SIZE 8
#define WRITE_VIA_CACHE_SIZE 4      /* Must be smaller than CACHE_SIZE */

struct unix_private_data {
      int   magic;
      int   dev;
      int   flags;
      int   access_time;
      struct unix_cache cache[CACHE_SIZE];
};

static errcode_t unix_open(const char *name, int flags, io_channel *channel);
static errcode_t unix_close(io_channel channel);
static errcode_t unix_set_blksize(io_channel channel, int blksize);
static errcode_t unix_read_blk(io_channel channel, unsigned long block,
                         int count, void *data);
static errcode_t unix_write_blk(io_channel channel, unsigned long block,
                        int count, const void *data);
static errcode_t unix_flush(io_channel channel);
static errcode_t unix_write_byte(io_channel channel, unsigned long offset,
                        int size, const void *data);

static struct struct_io_manager struct_unix_manager = {
      EXT2_ET_MAGIC_IO_MANAGER,
      "Unix I/O Manager",
      unix_open,
      unix_close,
      unix_set_blksize,
      unix_read_blk,
      unix_write_blk,
      unix_flush,
      unix_write_byte
};

io_manager unix_io_manager = &struct_unix_manager;

/*
 * Here are the raw I/O functions
 */
static errcode_t raw_read_blk(io_channel channel,
                        struct unix_private_data *data,
                        unsigned long block,
                        int count, void *buf)
{
      errcode_t   retval;
      size_t            size;
      ext2_loff_t location;
      int         actual = 0;

      size = (count < 0) ? -count : count * channel->block_size;
      location = (ext2_loff_t) block * channel->block_size;
      if (ext2fs_llseek(data->dev, location, SEEK_SET) != location) {
            retval = errno ? errno : EXT2_ET_LLSEEK_FAILED;
            goto error_out;
      }
      actual = read(data->dev, buf, size);
      if (actual != size) {
            if (actual < 0)
                  actual = 0;
            retval = EXT2_ET_SHORT_READ;
            goto error_out;
      }
      return 0;
      
error_out:
      memset((char *) buf+actual, 0, size-actual);
      if (channel->read_error)
            retval = (channel->read_error)(channel, block, count, buf,
                                     size, actual, retval);
      return retval;
}

static errcode_t raw_write_blk(io_channel channel,
                         struct unix_private_data *data,
                         unsigned long block,
                         int count, const void *buf)
{
      size_t            size;
      ext2_loff_t location;
      int         actual = 0;
      errcode_t   retval;

      if (count == 1)
            size = channel->block_size;
      else {
            if (count < 0)
                  size = -count;
            else
                  size = count * channel->block_size;
      }

      location = (ext2_loff_t) block * channel->block_size;
      if (ext2fs_llseek(data->dev, location, SEEK_SET) != location) {
            retval = errno ? errno : EXT2_ET_LLSEEK_FAILED;
            goto error_out;
      }
      
      actual = write(data->dev, buf, size);
      if (actual != size) {
            retval = EXT2_ET_SHORT_WRITE;
            goto error_out;
      }
      return 0;
      
error_out:
      if (channel->write_error)
            retval = (channel->write_error)(channel, block, count, buf,
                                    size, actual, retval);
      return retval;
}


/*
 * Here we implement the cache functions
 */

/* Allocate the cache buffers */
static errcode_t alloc_cache(io_channel channel,
                       struct unix_private_data *data)
{
      errcode_t         retval;
      struct unix_cache *cache;
      int               i;
      
      data->access_time = 0;
      for (i=0, cache = data->cache; i < CACHE_SIZE; i++, cache++) {
            cache->block = 0;
            cache->access_time = 0;
            cache->dirty = 0;
            cache->in_use = 0;
            if ((retval = ext2fs_get_mem(channel->block_size,
                                   (void **) &cache->buf)))
                  return retval;
      }
      return 0;
}

/* Free the cache buffers */
static void free_cache(io_channel channel, 
                   struct unix_private_data *data)
{
      struct unix_cache *cache;
      int               i;
      
      data->access_time = 0;
      for (i=0, cache = data->cache; i < CACHE_SIZE; i++, cache++) {
            cache->block = 0;
            cache->access_time = 0;
            cache->dirty = 0;
            cache->in_use = 0;
            if (cache->buf)
                  ext2fs_free_mem((void **) &cache->buf);
            cache->buf = 0;
      }
}

/*
 * Try to find a block in the cache.  If get_cache is non-zero, then
 * if the block isn't in the cache, evict the oldest block in the
 * cache and create a new cache entry for the requested block.
 */
static struct unix_cache *find_cached_block(io_channel channel,
                                  struct unix_private_data *data,
                                  unsigned long block,
                                  int get_cache)
{
      struct unix_cache *cache, *unused_cache, *oldest_cache;
      int               i;
      
      unused_cache = oldest_cache = 0;
      for (i=0, cache = data->cache; i < CACHE_SIZE; i++, cache++) {
            if (!cache->in_use) {
                  unused_cache = cache;
                  continue;
            }
            if (cache->block == block) {
                  cache->access_time = ++data->access_time;
                  return cache;
            }
            if (!oldest_cache ||
                (cache->access_time < oldest_cache->access_time))
                  oldest_cache = cache;
      }
      if (!get_cache)
            return 0;
      
      /*
       * Try to allocate cache slot.
       */
      if (unused_cache)
            cache = unused_cache;
      else {
            cache = oldest_cache;
            if (cache->dirty)
                  raw_write_blk(channel, data,
                              cache->block, 1, cache->buf);
      }
      cache->in_use = 1;
      cache->block = block;
      cache->access_time = ++data->access_time;
      return cache;
}

/*
 * Flush all of the blocks in the cache
 */
static errcode_t flush_cached_blocks(io_channel channel,
                             struct unix_private_data *data,
                             int invalidate)

{
      struct unix_cache *cache;
      errcode_t         retval, retval2;
      int               i;
      
      retval2 = 0;
      for (i=0, cache = data->cache; i < CACHE_SIZE; i++, cache++) {
            if (!cache->in_use)
                  continue;
            
            if (invalidate)
                  cache->in_use = 0;
            
            if (!cache->dirty)
                  continue;
            
            retval = raw_write_blk(channel, data,
                               cache->block, 1, cache->buf);
            if (retval)
                  retval2 = retval;
            else
                  cache->dirty = 0;
      }
      return retval2;
}



static errcode_t unix_open(const char *name, int flags, io_channel *channel)
{
      io_channel  io = NULL;
      struct unix_private_data *data = NULL;
      errcode_t   retval;
      int         open_flags;
      struct stat st;

      if (name == 0)
            return EXT2_ET_BAD_DEVICE_NAME;
      retval = ext2fs_get_mem(sizeof(struct struct_io_channel),
                        (void **) &io);
      if (retval)
            return retval;
      memset(io, 0, sizeof(struct struct_io_channel));
      io->magic = EXT2_ET_MAGIC_IO_CHANNEL;
      retval = ext2fs_get_mem(sizeof(struct unix_private_data),
                        (void **) &data);
      if (retval)
            goto cleanup;

      io->manager = unix_io_manager;
      retval = ext2fs_get_mem(strlen(name)+1, (void **) &io->name);
      if (retval)
            goto cleanup;

      strcpy(io->name, name);
      io->private_data = data;
      io->block_size = 1024;
      io->read_error = 0;
      io->write_error = 0;
      io->refcount = 1;

      memset(data, 0, sizeof(struct unix_private_data));
      data->magic = EXT2_ET_MAGIC_UNIX_IO_CHANNEL;

      if ((retval = alloc_cache(io, data)))
            goto cleanup;
      
      open_flags = (flags & IO_FLAG_RW) ? O_RDWR : O_RDONLY;
#ifdef HAVE_OPEN64
      data->dev = open64(name, open_flags);
#else
      data->dev = open(name, open_flags);
#endif
      if (data->dev < 0) {
            retval = errno;
            goto cleanup;
      }

#ifdef __linux__
#undef RLIM_INFINITY
#if (defined(__alpha__) || ((defined(__sparc__) || defined(__mips__)) && (SIZEOF_LONG == 4)))
#define RLIM_INFINITY   ((unsigned long)(~0UL>>1))
#else
#define RLIM_INFINITY  (~0UL)
#endif
      /*
       * Work around a bug in 2.4.10+ kernels where writes to block
       * devices are wrongly getting hit by the filesize limit.
       */
      if ((flags & IO_FLAG_RW) && 
          (fstat(data->dev, &st) == 0) &&
          (S_ISBLK(st.st_mode))) {
            struct rlimit     rlim;
            
            rlim.rlim_cur = rlim.rlim_max = (unsigned long) RLIM_INFINITY;
            setrlimit(RLIMIT_FSIZE, &rlim);
            getrlimit(RLIMIT_FSIZE, &rlim);
            if (((unsigned long) rlim.rlim_cur) <
                ((unsigned long) rlim.rlim_max)) {
                  rlim.rlim_cur = rlim.rlim_max;
                  setrlimit(RLIMIT_FSIZE, &rlim);
            }
      }
#endif
      *channel = io;
      return 0;

cleanup:
      if (data) {
            free_cache(io, data);
            ext2fs_free_mem((void **) &data);
      }
      if (io)
            ext2fs_free_mem((void **) &io);
      return retval;
}

static errcode_t unix_close(io_channel channel)
{
      struct unix_private_data *data;
      errcode_t   retval = 0;

      EXT2_CHECK_MAGIC(channel, EXT2_ET_MAGIC_IO_CHANNEL);
      data = (struct unix_private_data *) channel->private_data;
      EXT2_CHECK_MAGIC(data, EXT2_ET_MAGIC_UNIX_IO_CHANNEL);

      if (--channel->refcount > 0)
            return 0;

      retval = flush_cached_blocks(channel, data, 0);

      if (close(data->dev) < 0)
            retval = errno;
      free_cache(channel, data);

      ext2fs_free_mem((void **) &channel->private_data);
      if (channel->name)
            ext2fs_free_mem((void **) &channel->name);
      ext2fs_free_mem((void **) &channel);
      return retval;
}

static errcode_t unix_set_blksize(io_channel channel, int blksize)
{
      struct unix_private_data *data;
      errcode_t         retval;

      EXT2_CHECK_MAGIC(channel, EXT2_ET_MAGIC_IO_CHANNEL);
      data = (struct unix_private_data *) channel->private_data;
      EXT2_CHECK_MAGIC(data, EXT2_ET_MAGIC_UNIX_IO_CHANNEL);

      if (channel->block_size != blksize) {
            if ((retval = flush_cached_blocks(channel, data, 0)))
                  return retval;
            
            channel->block_size = blksize;
            free_cache(channel, data);
            if ((retval = alloc_cache(channel, data)))
                  return retval;
      }
      return 0;
}


static errcode_t unix_read_blk(io_channel channel, unsigned long block,
                         int count, void *buf)
{
      struct unix_private_data *data;
      struct unix_cache *cache;
      errcode_t   retval;
      char        *cp;
      int         i, j;

      EXT2_CHECK_MAGIC(channel, EXT2_ET_MAGIC_IO_CHANNEL);
      data = (struct unix_private_data *) channel->private_data;
      EXT2_CHECK_MAGIC(data, EXT2_ET_MAGIC_UNIX_IO_CHANNEL);

      /*
       * If we're doing an odd-sized read, flush out the cache and
       * then do a direct read.
       */
      if (count < 0) {
            if ((retval = flush_cached_blocks(channel, data, 0)))
                  return retval;
            return raw_read_blk(channel, data, block, count, buf);
      }

      cp = buf;
      while (count > 0) {
            /* If it's in the cache, use it! */
            if ((cache = find_cached_block(channel, data, block, 0))) {
#ifdef DEBUG
                  printf("Using cached block %d\n", block);
#endif
                  memcpy(cp, cache->buf, channel->block_size);
                  count--;
                  block++;
                  cp += channel->block_size;
                  continue;
            }
            /*
             * Find the number of uncached blocks so we can do a
             * single read request
             */
            for (i=1; i < count; i++)
                  if (find_cached_block(channel, data, block+i, 0))
                        break;
#ifdef DEBUG
            printf("Reading %d blocks starting at %d\n", i, block);
#endif
            if ((retval = raw_read_blk(channel, data, block, i, cp)))
                  return retval;
            
            /* Save the results in the cache */
            for (j=0; j < i; j++) {
                  count--;
                  cache = find_cached_block(channel, data, block++, 1);
                  if (cache)
                        memcpy(cache->buf, cp, channel->block_size);
                  cp += channel->block_size;
            }
      }
      return 0;
}

static errcode_t unix_write_blk(io_channel channel, unsigned long block,
                        int count, const void *buf)
{
      struct unix_private_data *data;
      struct unix_cache *cache;
      errcode_t   retval = 0, retval2;
      const char  *cp;
      int         writethrough;

      EXT2_CHECK_MAGIC(channel, EXT2_ET_MAGIC_IO_CHANNEL);
      data = (struct unix_private_data *) channel->private_data;
      EXT2_CHECK_MAGIC(data, EXT2_ET_MAGIC_UNIX_IO_CHANNEL);

      /*
       * If we're doing an odd-sized write or a very large write,
       * flush out the cache completely and then do a direct write.
       */
      if (count < 0 || count > WRITE_VIA_CACHE_SIZE) {
            if ((retval = flush_cached_blocks(channel, data, 1)))
                  return retval;
            return raw_write_blk(channel, data, block, count, buf);
      }

      /*
       * For a moderate-sized multi-block write, first force a write
       * if we're in write-through cache mode, and then fill the
       * cache with the blocks.
       */
      writethrough = channel->flags & CHANNEL_FLAGS_WRITETHROUGH;
      if (writethrough)
            retval = raw_write_blk(channel, data, block, count, buf);
      
      cp = buf;
      while (count > 0) {
            cache = find_cached_block(channel, data, block, 1);
            if (!cache) {
                  /*
                   * Oh shit, we couldn't get cache descriptor.
                   * Force the write directly.
                   */
                  if ((retval2 = raw_write_blk(channel, data, block,
                                    1, cp)))
                        retval = retval2;
            } else {
                  memcpy(cache->buf, cp, channel->block_size);
                  cache->dirty = !writethrough;
            }
            count--;
            block++;
            cp += channel->block_size;
      }
      return retval;
}

static errcode_t unix_write_byte(io_channel channel, unsigned long offset,
                         int size, const void *buf)
{
      struct unix_private_data *data;
      errcode_t   retval = 0;
      size_t            actual;

      EXT2_CHECK_MAGIC(channel, EXT2_ET_MAGIC_IO_CHANNEL);
      data = (struct unix_private_data *) channel->private_data;
      EXT2_CHECK_MAGIC(data, EXT2_ET_MAGIC_UNIX_IO_CHANNEL);

      /*
       * Flush out the cache completely
       */
      if ((retval = flush_cached_blocks(channel, data, 1)))
            return retval;

      if (lseek(data->dev, offset, SEEK_SET) < 0)
            return errno;
      
      actual = write(data->dev, buf, size);
      if (actual != size)
            return EXT2_ET_SHORT_WRITE;

      return 0;
}

/*
 * Flush data buffers to disk.  
 */
static errcode_t unix_flush(io_channel channel)
{
      struct unix_private_data *data;
      errcode_t retval = 0;
      
      EXT2_CHECK_MAGIC(channel, EXT2_ET_MAGIC_IO_CHANNEL);
      data = (struct unix_private_data *) channel->private_data;
      EXT2_CHECK_MAGIC(data, EXT2_ET_MAGIC_UNIX_IO_CHANNEL);

      retval = flush_cached_blocks(channel, data, 0);
      fsync(data->dev);
      return retval;
}


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