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Date: Fri, 26 Jul 2013 09:02:54 -0700
From: "Darrick J. Wong" <darrick.wong@...cle.com>
To: Robert Yang <liezhi.yang@...driver.com>
Cc: linux-ext4@...r.kernel.org, tytso@....edu, dvhart@...ux.intel.com
Subject: Re: [PATCH 2/2] debugfs.c: do sparse copy when src is a sparse file
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@...driver.com>
> Acked-by: Darren Hart <dvhart@...ux.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
>
> --
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