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fileio.c

Go to the documentation of this file.

/* 
   Copyright (C) Andrew Tridgell 1998
   Copyright (C) 2002 by Martin Pool
   
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.
   
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
   
   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/

/*
  File IO utilities used in rsync 
  */
#include "rsync.h"

static char last_byte;
static int last_sparse;
extern int sparse_files;

int sparse_end(int f)
{
        if (last_sparse) {
                do_lseek(f,-1,SEEK_CUR);
                return (write(f,&last_byte,1) == 1 ? 0 : -1);
        }
        last_sparse = 0;
        return 0;
}


static int write_sparse(int f,char *buf,size_t len)
{
        size_t l1=0, l2=0;
        int ret;

        for (l1=0;l1<len && buf[l1]==0;l1++) ;
        for (l2=0;l2<(len-l1) && buf[len-(l2+1)]==0;l2++) ;

        last_byte = buf[len-1];

        if (l1 == len || l2 > 0)
                last_sparse=1;

        if (l1 > 0) {
                do_lseek(f,l1,SEEK_CUR);  
        }

        if (l1 == len) 
                return len;

        ret = write(f, buf + l1, len - (l1+l2));
        if (ret == -1 || ret == 0)
                return ret;
        else if (ret != (int) (len - (l1+l2))) 
                return (l1+ret);

        if (l2 > 0)
                do_lseek(f,l2,SEEK_CUR);
        
        return len;
}



int write_file(int f,char *buf,size_t len)
{
        int ret = 0;

        if (!sparse_files) {
                return write(f,buf,len);
        }

        while (len>0) {
                int len1 = MIN(len, SPARSE_WRITE_SIZE);
                int r1 = write_sparse(f, buf, len1);
                if (r1 <= 0) {
                        if (ret > 0) return ret;
                        return r1;
                }
                len -= r1;
                buf += r1;
                ret += r1;
        }
        return ret;
}



/* this provides functionality somewhat similar to mmap() but using
   read(). It gives sliding window access to a file. mmap() is not
   used because of the possibility of another program (such as a
   mailer) truncating the file thus giving us a SIGBUS */
struct map_struct *map_file(int fd,OFF_T len)
{
        struct map_struct *map;
        map = (struct map_struct *)malloc(sizeof(*map));
        if (!map) out_of_memory("map_file");

        map->fd = fd;
        map->file_size = len;
        map->p = NULL;
        map->p_size = 0;
        map->p_offset = 0;
        map->p_fd_offset = 0;
        map->p_len = 0;

        return map;
}

/* slide the read window in the file */
char *map_ptr(struct map_struct *map,OFF_T offset,int len)
{
        int nread;
        OFF_T window_start, read_start;
        int window_size, read_size, read_offset;

        if (len == 0) {
                return NULL;
        }

        /* can't go beyond the end of file */
        if (len > (map->file_size - offset)) {
                len = map->file_size - offset;
        }

        /* in most cases the region will already be available */
        if (offset >= map->p_offset && 
            offset+len <= map->p_offset+map->p_len) {
                return (map->p + (offset - map->p_offset));
        }


        /* nope, we are going to have to do a read. Work out our desired window */
        if (offset > 2*CHUNK_SIZE) {
                window_start = offset - 2*CHUNK_SIZE;
                window_start &= ~((OFF_T)(CHUNK_SIZE-1)); /* assumes power of 2 */
        } else {
                window_start = 0;
        }
        window_size = MAX_MAP_SIZE;
        if (window_start + window_size > map->file_size) {
                window_size = map->file_size - window_start;
        }
        if (offset + len > window_start + window_size) {
                window_size = (offset+len) - window_start;
        }

        /* make sure we have allocated enough memory for the window */
        if (window_size > map->p_size) {
                map->p = (char *)Realloc(map->p, window_size);
                if (!map->p) out_of_memory("map_ptr");
                map->p_size = window_size;
        }

        /* now try to avoid re-reading any bytes by reusing any bytes from the previous
           buffer. */
        if (window_start >= map->p_offset &&
            window_start < map->p_offset + map->p_len &&
            window_start + window_size >= map->p_offset + map->p_len) {
                read_start = map->p_offset + map->p_len;
                read_offset = read_start - window_start;
                read_size = window_size - read_offset;
                memmove(map->p, map->p + (map->p_len - read_offset), read_offset);
        } else {
                read_start = window_start;
                read_size = window_size;
                read_offset = 0;
        }

        if (read_size <= 0) {
                rprintf(FINFO,"Warning: unexpected read size of %d in map_ptr\n", read_size);
        } else {
                if (map->p_fd_offset != read_start) {
                        if (do_lseek(map->fd,read_start,SEEK_SET) != read_start) {
                                rprintf(FERROR,"lseek failed in map_ptr\n");
                                exit_cleanup(RERR_FILEIO);
                        }
                        map->p_fd_offset = read_start;
                }

                if ((nread=read(map->fd,map->p + read_offset,read_size)) != read_size) {
                        if (nread < 0) nread = 0;
                        /* the best we can do is zero the buffer - the file
                           has changed mid transfer! */
                        memset(map->p+read_offset+nread, 0, read_size - nread);
                }
                map->p_fd_offset += nread;
        }

        map->p_offset = window_start;
        map->p_len = window_size;
  
        return map->p + (offset - map->p_offset); 
}


void unmap_file(struct map_struct *map)
{
        if (map->p) {
                free(map->p);
                map->p = NULL;
        }
        memset(map, 0, sizeof(*map));
        free(map);
}

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