ioctl_xfs_getbmapx — query extent information for an open file
Synopsis
#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);
Description
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:
- bmv_offset
The file offset of the area of interest in the file.
- bmv_length
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.
- bmv_count
The number of elements in the array, including this header. The minimum value is 2.
- bmv_entries
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.
- bmv_iflags
-
For the XFS_IOC_GETBMAPX function, this is a bitmask containing a combination of the following flags:
- BMV_IF_ATTRFORK
Return information about the extended attribute fork.
- BMV_IF_PREALLOC
Return information about unwritten pre-allocated segments.
- BMV_IF_DELALLOC
Return information about delayed allocation reservation segments.
- BMV_IF_NO_HOLES
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:
- bmv_offset
File offset of segment.
- bmv_block
Physical starting block of segment. If this is -1, then the segment is a hole.
- bmv_length
Length of segment.
- bmv_oflags
-
The XFS_IOC_GETBMAPX function will fill this field with a combination of the following flags:
- BMV_OF_PREALLOC
The segment is an unwritten pre-allocation.
- BMV_OF_DELALLOC
The segment is a delayed allocation reservation.
- BMV_OF_LAST
This segment is the last in the file.
- BMV_OF_SHARED
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.
Return Value
On error, -1 is returned, and errno is set to indicate the error.
Errors
Error codes can be one of, but are not limited to, the following:
- EFAULT
The kernel was not able to copy into the userspace buffer.
- EFSBADCRC
Metadata checksum validation failed while performing the query.
- EFSCORRUPTED
Metadata corruption was encountered while performing the query.
- EINVAL
One of the arguments was not valid.
- EIO
An I/O error was encountered while performing the query.
- ENOMEM
There was insufficient memory to perform the query.
Conforming to
This API is specific to XFS filesystem on the Linux kernel.