The phaseout of the mmap() file operation
6 days ago
- #mmap
- #Memory Management
- #Linux Kernel
- The mmap() file operation was introduced in Linux kernel version 0.98.2 in 1992.
- The mmap() method allows drivers to set up memory mappings but has issues like complex cleanup on failure and direct access to memory-management structures.
- A new mmap_prepare() callback was introduced in kernel 6.17 to replace mmap(), providing a cleaner API with less cleanup overhead.
- The vm_area_desc structure in mmap_prepare() limits driver access to only necessary information for setting up mappings.
- Further enhancements include the mmap_action structure for more complex driver needs, such as remapping address ranges.
- The transition from mmap() to mmap_prepare() is ongoing, with many drivers still needing conversion.
- The /dev/zero driver exhibits unique behavior in its mmap() implementation, described as 'very unique and rather concerning'.