---
name: "ioctl_xfs_getresblks"
section: "2"
platform: "linux"
package: "xfsprogs"
version: "7.2.1-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/ioctl_xfs_getresblks"
---

# ioctl\_xfs\_getresblks(2)

query and set XFS free space reservation information

## NAME

ioctl\_xfs\_getresblks - query and set XFS free space reservation information

## SYNOPSIS

**#include \<xfs/xfs\_fs.h\>**

**int ioctl(int** *fd***, XFS\_IOC\_GET\_RESBLKS, struct xfs\_fsop\_resblks \****arg***);**\
 **int ioctl(int** *fd***, XFS\_IOC\_SET\_RESBLKS, struct xfs\_fsop\_resblks \****arg***);**

## DESCRIPTION

Query or set the free space reservation information. These blocks are reserved by the filesystem as a final attempt to prevent metadata update failures due to insufficient space. Only the system administrator can use these ioctls, because overriding the defaults is extremely dangerous.

This functionality is intended only for use by XFS filesystem developers.

The reservation information is conveyed in a structure of the following form:

```
struct xfs_fsop_resblks {
	__u64  resblks;
	__u64  resblks_avail;
};
```

*resblks* is the number of blocks that the filesystem will try to maintain to prevent critical out of space situations.

*resblks\_avail* is the number of reserved blocks remaining.

## 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:

- **EFSBADCRC**

  Metadata checksum validation failed while performing the query.

- **EFSCORRUPTED**

  Metadata corruption was encountered while performing the query.

- **EINVAL**

  The specified allocation group number is not valid for this filesystem.

- **EIO**

  An I/O error was encountered while performing the query.

- **EPERM**

  Caller does not have permission to call this ioctl.

## CONFORMING TO

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

## SEE ALSO

[**ioctl**(2)](/ioctl/2.md)