file.c

编译后直接运行的ＭＰ３播放器全部Ｃ语言源代码 一个包含FAT文件系统、系统引导 Boot、FLASH Driver等内容的

    }

    return 0;
}

int ftruncate(int fd, off_t size)
{
    int rc, sector;
    struct filedesc* file = &openfiles[fd];

    sector = size / SECTOR_SIZE;
    if (size % SECTOR_SIZE)
        sector++;

    rc = fat_seek(&(file->fatfile), sector);
    if (rc < 0) {
        errno = EIO;
        return rc * 10 - 1;
    }

    rc = fat_truncate(&(file->fatfile));
    if (rc < 0) {
        errno = EIO;
        return rc * 10 - 2;
    }

    file->size = size;

    return 0;
}

static int flush_cache(int fd)
{
    int rc;
    struct filedesc* file = &openfiles[fd];
    int sector = file->fileoffset / SECTOR_SIZE;
      
    DEBUGF("Flushing dirty sector cache\n");
        
    /* make sure we are on correct sector */
    rc = fat_seek(&(file->fatfile), sector);
    if ( rc < 0 )
        return rc * 10 - 3;

    rc = fat_readwrite(&(file->fatfile), 1,
                       file->cache, true );

    if ( rc < 0 ) {
        if(file->fatfile.eof)
            errno = ENOSPC;

        return rc * 10 - 2;
    }

    file->dirty = false;

    return 0;
}

static int readwrite(int fd, void* buf, int count, bool write)
{
    int sectors;
    int nread=0;
    struct filedesc* file = &openfiles[fd];
    int rc;

    if ( !file->busy ) {
        errno = EBADF;
        return -1;
    }

    LDEBUGF( "readwrite(%d,%x,%d,%s)\n",
             fd,buf,count,write?"write":"read");

    /* attempt to read past EOF? */
    if (!write && count > file->size - file->fileoffset)
        count = file->size - file->fileoffset;

    /* any head bytes? */
    if ( file->cacheoffset != -1 ) {
        int headbytes;
        int offs = file->cacheoffset;
        if ( count <= SECTOR_SIZE - file->cacheoffset ) {
            headbytes = count;
            file->cacheoffset += count;
            if ( file->cacheoffset >= SECTOR_SIZE )
                file->cacheoffset = -1;
        }
        else {
            headbytes = SECTOR_SIZE - file->cacheoffset;
            file->cacheoffset = -1;
        }

        if (write) {
            memcpy( file->cache + offs, buf, headbytes );
            if (offs+headbytes == SECTOR_SIZE) {
                int rc = flush_cache(fd);
                if ( rc < 0 ) {
                    errno = EIO;
                    return rc * 10 - 2;
                }
                file->cacheoffset = -1;
            }
            else
                file->dirty = true;
        }
        else {
            memcpy( buf, file->cache + offs, headbytes );
        }

        nread = headbytes;
        count -= headbytes;
    }

    /* if buffer has been modified, write it back to disk */
    if (nread && file->dirty) {
        rc = flush_cache(fd);
        if (rc < 0)
            return rc * 10 - 3;
    }

    /* read/write whole sectors right into/from the supplied buffer */
    sectors = count / SECTOR_SIZE;
    if ( sectors ) {
        int rc = fat_readwrite(&(file->fatfile), sectors, buf+nread, write );
        if ( rc < 0 ) {
            DEBUGF("Failed read/writing %d sectors\n",sectors);
            errno = EIO;
            if(write && file->fatfile.eof) {
                DEBUGF("No space left on device\n");
                errno = ENOSPC;
            } else {
                file->fileoffset += nread;
            }
            file->cacheoffset = -1;
            return nread ? nread : rc * 10 - 4;
        }
        else {
            if ( rc > 0 ) {
                nread += rc * SECTOR_SIZE;
                count -= sectors * SECTOR_SIZE;

                /* if eof, skip tail bytes */
                if ( rc < sectors )
                    count = 0;
            }
            else {
                /* eof */
                count=0;
            }

            file->cacheoffset = -1;
        }
    }

    /* any tail bytes? */
    if ( count ) {
        if (write) {
            if ( file->fileoffset + nread < file->size ) {
                /* sector is only partially filled. copy-back from disk */
                int rc;
                LDEBUGF("Copy-back tail cache\n");
                rc = fat_readwrite(&(file->fatfile), 1, file->cache, false );
                if ( rc < 0 ) {
                    DEBUGF("Failed writing\n");
                    errno = EIO;
                    file->fileoffset += nread;
                    file->cacheoffset = -1;
                    return nread ? nread : rc * 10 - 5;
                }
                /* seek back one sector to put file position right */
                rc = fat_seek(&(file->fatfile), 
                              (file->fileoffset + nread) / 
                              SECTOR_SIZE);
                if ( rc < 0 ) {
                    DEBUGF("fat_seek() failed\n");
                    errno = EIO;
                    file->fileoffset += nread;
                    file->cacheoffset = -1;
                    return nread ? nread : rc * 10 - 6;
                }
            }
            memcpy( file->cache, buf + nread, count );
            file->dirty = true;
        }
        else {
            rc = fat_readwrite(&(file->fatfile), 1, &(file->cache),false);
            if (rc < 1 ) {
                DEBUGF("Failed caching sector\n");
                errno = EIO;
                file->fileoffset += nread;
                file->cacheoffset = -1;
                return nread ? nread : rc * 10 - 7;
            }
            memcpy( buf + nread, file->cache, count );
        }
            
        nread += count;
        file->cacheoffset = count;
    }

    file->fileoffset += nread;
    LDEBUGF("fileoffset: %d\n", file->fileoffset);

    /* adjust file size to length written */
    if ( write && file->fileoffset > file->size )
        file->size = file->fileoffset;

    return nread;
}

ssize_t write(int fd, const void* buf, size_t count)
{
    if (!openfiles[fd].write) {
        errno = EACCES;
        return -1;
    }
    return readwrite(fd, (void *)buf, count, true);
}

ssize_t read(int fd, void* buf, size_t count)
{
    return readwrite(fd, buf, count, false);
}


off_t lseek(int fd, off_t offset, int whence)
{
    int pos;
    int newsector;
    int oldsector;
    int sectoroffset;
    int rc;
    struct filedesc* file = &openfiles[fd];

    LDEBUGF("lseek(%d,%d,%d)\n",fd,offset,whence);

    if ( !file->busy ) {
        errno = EBADF;
        return -1;
    }

    switch ( whence ) {
        case SEEK_SET:
            pos = offset;
            break;

        case SEEK_CUR:
            pos = file->fileoffset + offset;
            break;

        case SEEK_END:
            pos = file->size + offset;
            break;

        default:
            errno = EINVAL;
            return -2;
    }
    if ((pos < 0) || (pos > file->size)) {
        errno = EINVAL;
        return -3;
    }

    /* new sector? */
    newsector = pos / SECTOR_SIZE;
    oldsector = file->fileoffset / SECTOR_SIZE;
    sectoroffset = pos % SECTOR_SIZE;

    if ( (newsector != oldsector) ||
         ((file->cacheoffset==-1) && sectoroffset) ) {

        if ( newsector != oldsector ) {
            if (file->dirty) {
                rc = flush_cache(fd);
                if (rc < 0)
                    return rc * 10 - 5;
            }
            
            rc = fat_seek(&(file->fatfile), newsector);
            if ( rc < 0 ) {
                errno = EIO;
                return rc * 10 - 4;
            }
        }
        if ( sectoroffset ) {
            rc = fat_readwrite(&(file->fatfile), 1,
                               &(file->cache),false);
            if ( rc < 0 ) {
                errno = EIO;
                return rc * 10 - 6;
            }
            file->cacheoffset = sectoroffset;
        }
        else
            file->cacheoffset = -1;
    }
    else
        if ( file->cacheoffset != -1 )
            file->cacheoffset = sectoroffset;

    file->fileoffset = pos;

    return pos;
}

int filesize(int fd)
{
    struct filedesc* file = &openfiles[fd];

    if ( !file->busy ) {
        errno = EBADF;
        return -1;
    }
    
    return file->size;
}