Re: [PATCH 2/2] debugfs.c: do sparse copy when src is a sparse file

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Fri, Jul 26, 2013 at 06:30:57PM +0800, Robert Yang wrote:
> Let debugfs do sparse copy when src is a sparse file, just like
> "cp --sparse=auto"
> 
> * For the:
>   #define IO_BUFSIZE 64*1024
>   this is a suggested value from gnu coreutils:
>   http://git.savannah.gnu.org/gitweb/?p=coreutils.git;a=blob;f=src/ioblksize.h;h=1ae93255e7d0ccf0855208c7ae5888209997bf16;hb=HEAD
> 
> * Use malloc() to allocate memory for the buffer since put 64K (or
>   more) on the stack seems not a good idea.
> 
> Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
> Acked-by: Darren Hart <dvhart@linux.intel.com>
> ---
>  debugfs/debugfs.c | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 53 insertions(+), 5 deletions(-)
> 
> diff --git a/debugfs/debugfs.c b/debugfs/debugfs.c
> index b77d0b5..0379f38 100644
> --- a/debugfs/debugfs.c
> +++ b/debugfs/debugfs.c
> @@ -37,6 +37,16 @@ extern char *optarg;
>  #include "../version.h"
>  #include "jfs_user.h"
>  
> +/* 64KiB is the minimium blksize to best minimize system call overhead. */
> +#ifndef IO_BUFSIZE
> +#define IO_BUFSIZE 64*1024
> +#endif
> +
> +/* Block size for `st_blocks' */
> +#ifndef S_BLKSIZE
> +#define S_BLKSIZE 512
> +#endif
> +
>  ss_request_table *extra_cmds;
>  const char *debug_prog_name;
>  int sci_idx;
> @@ -1571,22 +1581,28 @@ void do_find_free_inode(int argc, char *argv[])
>  }
>  
>  #ifndef READ_ONLY
> -static errcode_t copy_file(int fd, ext2_ino_t newfile)
> +static errcode_t copy_file(int fd, ext2_ino_t newfile, int bufsize, int make_holes)
>  {
>  	ext2_file_t	e2_file;
>  	errcode_t	retval;
>  	int		got;
>  	unsigned int	written;
> -	char		buf[8192];
> +	char		*buf;
>  	char		*ptr;
> +	char		*zeromem;
> +	int		cmp;
>  
>  	retval = ext2fs_file_open(current_fs, newfile,
>  				  EXT2_FILE_WRITE, &e2_file);
>  	if (retval)
>  		return retval;
>  
> +	if (!(buf = (char *) malloc(bufsize))){
> +		fprintf(stderr, "copy_file: can't allocate buffer\n");
> +		return;
> +	}
>  	while (1) {
> -		got = read(fd, buf, sizeof(buf));
> +		got = read(fd, buf, bufsize);
>  		if (got == 0)
>  			break;
>  		if (got < 0) {
> @@ -1594,20 +1610,42 @@ static errcode_t copy_file(int fd, ext2_ino_t newfile)
>  			goto fail;
>  		}
>  		ptr = buf;
> +
> +		/* Sparse copy */
> +		if (make_holes) {
> +			if (!(zeromem = (char *) calloc(got, 1))) {

Maybe ext2fs_get_memzero()?  And I suspect you can allocate a bufsize-sized
zeromem outside the while loop.  Chances are pretty good that if make_holes,
then buf_size won't be greater than 4096 anyway.

--D

> +				fprintf(stderr, "copy_file: can't allocate buffer\n");
> +				return;
> +			}
> +			/* Check whether all is zero */
> +			cmp = memcmp(ptr, zeromem, got);
> +			/* Free it as early as possible */
> +			free(zeromem);
> +			if (cmp == 0) {
> +				 /* The whole block is zero, make a hole */
> +				retval = ext2fs_file_lseek(e2_file, got, EXT2_SEEK_CUR, NULL);
> +				if (retval)
> +					goto fail;
> +				got = 0;
> +			}
> +		}
> +
> +		/* Normal copy */
>  		while (got > 0) {
>  			retval = ext2fs_file_write(e2_file, ptr,
>  						   got, &written);
>  			if (retval)
>  				goto fail;
> -
>  			got -= written;
>  			ptr += written;
>  		}
>  	}
> +	free(buf);
>  	retval = ext2fs_file_close(e2_file);
>  	return retval;
>  
>  fail:
> +	free(buf);
>  	(void) ext2fs_file_close(e2_file);
>  	return retval;
>  }
> @@ -1620,6 +1658,8 @@ void do_write(int argc, char *argv[])
>  	ext2_ino_t	newfile;
>  	errcode_t	retval;
>  	struct ext2_inode inode;
> +	int		bufsize = IO_BUFSIZE;
> +	int		make_holes = 0;
>  
>  	if (common_args_process(argc, argv, 3, 3, "write",
>  				"<native file> <new file>", CHECK_FS_RW))
> @@ -1684,7 +1724,15 @@ void do_write(int argc, char *argv[])
>  		return;
>  	}
>  	if (LINUX_S_ISREG(inode.i_mode)) {
> -		retval = copy_file(fd, newfile);
> +		if (statbuf.st_blocks < statbuf.st_size / S_BLKSIZE) {
> +			make_holes = 1;
> +			/*
> +			 * Use I/O blocksize as buffer size when
> +			 * copying sparse files.
> +			 */
> +			bufsize = statbuf.st_blksize;
> +		}
> +		retval = copy_file(fd, newfile, bufsize, make_holes);
>  		if (retval)
>  			com_err("copy_file", retval, 0);
>  	}
> -- 
> 1.8.1.2
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html