[LU-16480] Lustre fiemap does not properly handle fm_extent_count=0

• Type: Bug
• Resolution: Fixed
• Priority: Major
• Fix Version/s: Lustre 2.16.0, Lustre 2.15.5
• Labels: patch
• Severity: 3
• Assignee: Andrew Perepechko
• Reporter: Andrew Perepechko

Description

"fm_extent_count specifies the number of elements in the fm_extents[] array that can be used to return extents. If fm_extent_count is zero, then the fm_extents[] array is ignored (no extents will be returned), and the fm_mapped_extents count will hold the number of extents needed in fm_extents[] to hold the file’s current mapping."

 

https://www.kernel.org/doc/html/latest/filesystems/fiemap.html

 

In practice, depending on the state of the kernel thread stack, EINVAL can be returned to userspace even for simple single stripe files.

 

Details will follow.

Issue Links

• is related to: LU-17110 Slab corruption using fiemap ioctl with fm_extent_count==0