Re: [RFC] btrfs-progs: cmds: Add subcommand that dumps file extents

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

On 2021/7/10 下午10:41, Sidong Yang wrote:
> This patch adds an subcommand in inspect-internal. It dumps file extents of
> the file that user provided. It helps to show the internal information
> about file extents comprise the file.

So this is going to be the combined command of filemap + btrfs-map-logical.

But how do you handle dirty pages which hasn't yet been flushed to disk?

Thanks,
Qu
>
> Signed-off-by: Sidong Yang <realwakka@gmail.com>
> ---
> Hi, I'm writing an patch that adds an subcommand that dumps file extents of
> the file. I don't have much idea about btrfs but I referenced btrfs
> wiki, dev-docs, and also Zygo's bee. It's just like draft.
>
> I have some questions below.
>
> The command works like below,
> # ./btrfs inspect-internal dump-file-extents /mnt/bb/TAGS
> begin = 0x0, end = 0x20000, physical = 0x4fdf5000, physical_len = 0xc000
> begin = 0x20000, end = 0x40000, physical = 0x4fe01000, physical_len = 0xc000
> begin = 0x40000, end = 0x47000, physical = 0x4fe0d000, physical_len = 0x3000
>
> What format would be better?
> Is it better to just use the variable name as it is? like disk_bytenr
> not like physical_len?
>
> And what option do we need? like showing compression or file extent type?
>
> Any comments will be welcome. Thanks!
> ---
>   Makefile                         |   2 +-
>   cmds/commands.h                  |   2 +-
>   cmds/inspect-dump-file-extents.c | 130 +++++++++++++++++++++++++++++++
>   cmds/inspect.c                   |   1 +
>   4 files changed, 133 insertions(+), 2 deletions(-)
>   create mode 100644 cmds/inspect-dump-file-extents.c
>
> diff --git a/Makefile b/Makefile
> index a1cc457b..911e16de 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -156,7 +156,7 @@ cmds_objects = cmds/subvolume.o cmds/filesystem.o cmds/device.o cmds/scrub.o \
>   	       cmds/restore.o cmds/rescue.o cmds/rescue-chunk-recover.o \
>   	       cmds/rescue-super-recover.o \
>   	       cmds/property.o cmds/filesystem-usage.o cmds/inspect-dump-tree.o \
> -	       cmds/inspect-dump-super.o cmds/inspect-tree-stats.o cmds/filesystem-du.o \
> +	       cmds/inspect-dump-super.o cmds/inspect-tree-stats.o cmds/inspect-dump-file-extents.o cmds/filesystem-du.o \
>   	       mkfs/common.o check/mode-common.o check/mode-lowmem.o
>   libbtrfs_objects = common/send-stream.o common/send-utils.o kernel-lib/rbtree.o btrfs-list.o \
>   		   kernel-lib/radix-tree.o common/extent-cache.o kernel-shared/extent_io.o \
> diff --git a/cmds/commands.h b/cmds/commands.h
> index 8fa85d6c..55de248e 100644
> --- a/cmds/commands.h
> +++ b/cmds/commands.h
> @@ -154,5 +154,5 @@ DECLARE_COMMAND(select_super);
>   DECLARE_COMMAND(dump_super);
>   DECLARE_COMMAND(debug_tree);
>   DECLARE_COMMAND(rescue);
> -
> +DECLARE_COMMAND(inspect_dump_file_extents);
>   #endif
> diff --git a/cmds/inspect-dump-file-extents.c b/cmds/inspect-dump-file-extents.c
> new file mode 100644
> index 00000000..99aec7d7
> --- /dev/null
> +++ b/cmds/inspect-dump-file-extents.c
> @@ -0,0 +1,130 @@
> +/*
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public
> + * License v2 as published by the Free Software Foundation.
> + *
> + * 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., 59 Temple Place - Suite 330,
> + * Boston, MA 021110-1307, USA.
> + */
> +
> +#include <unistd.h>
> +#include <stdio.h>
> +#include <fcntl.h>
> +
> +#include <sys/ioctl.h>
> +
> +#include "common/utils.h"
> +#include "cmds/commands.h"
> +
> +static const char * const cmd_inspect_dump_file_extents_usage[] = {
> +	"btrfs inspect-internal dump-extent path",
> +	"Dump file extent in a textual form",
> +	NULL
> +};
> +
> +static int cmd_inspect_dump_file_extents(const struct cmd_struct *cmd,
> +										 int argc, char **argv)
> +{
> +	int fd;
> +	struct stat statbuf;
> +	struct btrfs_ioctl_ino_lookup_args lookup;
> +	struct btrfs_ioctl_search_args args;
> +	struct btrfs_ioctl_search_key *sk = &args.key;
> +	struct btrfs_file_extent_item *extent_item;
> +	struct btrfs_ioctl_search_header *header;
> +	u64 pos;
> +	u64 buf_off;
> +	u64 len;
> +	u64 begin;
> +	u64 physical;
> +	u64 offset;
> +	u64 physical_len;
> +	int ret;
> +	int i;
> +
> +	fd = open(argv[optind], O_RDONLY);
> +	if (fd < 0) {
> +		error("cannot open %s: %m", argv[optind]);
> +		ret = 1;
> +		goto out;
> +	}
> +
> +	if (fstat(fd, &statbuf) < 0) {
> +		error("failed to fstat %s: %m", argv[optind]);
> +		ret = 1;
> +		goto out;
> +	}
> +
> +	lookup.treeid = 0;
> +	lookup.objectid = BTRFS_FIRST_FREE_OBJECTID;
> +
> +	if (ioctl(fd, BTRFS_IOC_INO_LOOKUP, &lookup) < 0) {
> +		error("failed to lookup inode %s: %m", argv[optind]);
> +		ret = 1;
> +		goto out;
> +	}
> +
> +	pos = 0;
> +
> +	sk->tree_id = lookup.treeid;
> +	sk->min_objectid = statbuf.st_ino;
> +	sk->max_objectid = statbuf.st_ino;
> +
> +	sk->max_offset = UINT64_MAX;
> +	sk->min_transid = 0;
> +	sk->max_transid = UINT64_MAX;
> +	sk->min_type = sk->max_type = BTRFS_EXTENT_DATA_KEY;
> +	sk->nr_items = 4096;
> +
> +	while (statbuf.st_size > pos) {
> +		sk->min_offset = pos;
> +		if (ioctl(fd, BTRFS_IOC_TREE_SEARCH, &args)) {
> +			error("failed to search tree ioctl %s: %m", argv[optind]);
> +			ret = 1;
> +			goto out;
> +		}
> +
> +		buf_off = 0;
> +		for(i=0; i<sk->nr_items; ++i) {
> +			header = (struct btrfs_ioctl_search_header *)(args.buf + buf_off);
> +
> +			if (btrfs_search_header_type(header) == BTRFS_EXTENT_DATA_KEY) {
> +				extent_item = (struct btrfs_file_extent_item *)(header + 1);
> +				begin = btrfs_search_header_offset(header);
> +
> +				printf("begin = 0x%llx, ", begin);
> +				switch (extent_item->type) {
> +				case BTRFS_FILE_EXTENT_INLINE:
> +					len = le64_to_cpu(extent_item->ram_bytes);
> +					printf("end = 0x%llx\n", begin + len);
> +					break;
> +				case BTRFS_FILE_EXTENT_REG:
> +				case BTRFS_FILE_EXTENT_PREALLOC:
> +					len = le64_to_cpu(extent_item->num_bytes);
> +					physical = le64_to_cpu(extent_item->disk_bytenr);
> +					physical_len = le64_to_cpu(extent_item->disk_num_bytes);
> +					offset = le64_to_cpu(extent_item->offset);
> +					printf("end = 0x%llx, physical = 0x%llx, physical_len = 0x%llx\n",
> +						   begin + len, physical, physical_len);
> +					break;
> +				}
> +
> +			}
> +			buf_off += sizeof(*header) + btrfs_search_header_len(header);
> +			pos += len;
> +		}
> +
> +	}
> +	ret = 0;
> +out:
> +	close(fd);
> +	return ret;
> +}
> +DEFINE_SIMPLE_COMMAND(inspect_dump_file_extents, "dump-file-extents");
> diff --git a/cmds/inspect.c b/cmds/inspect.c
> index 2ef5f4b6..dfb0e27b 100644
> --- a/cmds/inspect.c
> +++ b/cmds/inspect.c
> @@ -696,6 +696,7 @@ static const struct cmd_group inspect_cmd_group = {
>   		&cmd_struct_inspect_dump_tree,
>   		&cmd_struct_inspect_dump_super,
>   		&cmd_struct_inspect_tree_stats,
> +		&cmd_struct_inspect_dump_file_extents,
>   		NULL
>   	}
>   };
>