Scroll to navigation



ioctl_xfs_getbmapx - query extent information for an open file


#include <xfs/xfs_fs.h>

int ioctl(int fd, XFS_IOC_GETBMAP, struct getbmap *arg);
int ioctl(int fd, XFS_IOC_GETBMAPA, struct getbmap *arg);
int ioctl(int fd, XFS_IOC_GETBMAPX, struct getbmapx *arg);


Get the block map for a segment of a file in an XFS file system. The mapping information is conveyed via an array of structures of the following form:

struct getbmap {
	__s64   bmv_offset;
	__s64   bmv_block;
	__s64   bmv_length;
	__s32   bmv_count;
	__s32   bmv_entries;

The XFS_IOC_GETBMAPX ioctl uses a larger version of that structure:

struct getbmapx {
	__s64   bmv_offset;
	__s64   bmv_block;
	__s64   bmv_length;
	__s32   bmv_count;
	__s32   bmv_entries;
	__s32   bmv_iflags;
	__s32   bmv_oflags;
	__s32   bmv_unused1;
	__s32   bmv_unused2;

All sizes and offsets in the structure are in units of 512 bytes.

The first structure in the array is a header and the remaining structures in the array contain block map information on return. The header controls iterative calls to the command and should be filled out as follows:

The file offset of the area of interest in the file.
The length of the area of interest in the file. If this value is set to -1, the length of the interesting area is the rest of the file.
The number of elements in the array, including this header. The minimum value is 2.
The number of entries actually filled in by the call. This does not need to be filled out before the call. This value may be zero if no extents were found in the requested range, or if iterated calls have reached the end of the requested range.
For the XFS_IOC_GETBMAPX function, this is a bitmask containing a combination of the following flags:
Return information about the extended attribute fork.
Return information about unwritten pre-allocated segments.
Return information about delayed allocation reservation segments.
Do not return information about holes.

The other bmv_* fields in the header are ignored.

On successful return from a call, the offset and length values in the header are updated so that the command can be reused to obtain more information. The remaining elements of the array will be filled out by the call as follows:

File offset of segment.
Physical starting block of segment. If this is -1, then the segment is a hole.
Length of segment.
The XFS_IOC_GETBMAPX function will fill this field with a combination of the following flags:
The segment is an unwritten pre-allocation.
The segment is a delayed allocation reservation.
This segment is the last in the file.
This segment shares blocks with other files.

The other bmv_* fields are unused in the array of output records.

The XFS_IOC_GETBMAPA command is identical to XFS_IOC_GETBMAP except that information about the attribute fork of the file is returned.


On error, -1 is returned, and errno is set to indicate the error.


Error codes can be one of, but are not limited to, the following:

The kernel was not able to copy into the userspace buffer.
Metadata checksum validation failed while performing the query.
Metadata corruption was encountered while performing the query.
One of the arguments was not valid.
An I/O error was encountered while performing the query.
There was insufficient memory to perform the query.


This API is specific to XFS filesystem on the Linux kernel.



2019-06-17 XFS