How Linux Kernel's Devres Mechanism Automates Driver Resource Cleanup

Devres, introduced by Tejun Heo in 2007 during libata's conversion, is the Linux kernel's system for automatically managing device resource cleanup through functions prefixed with 'devm_'. Every managed allocation is registered on a per-device list, and the driver core automatically releases all entries in reverse order when a probe fails or a device unbinds. This eliminates the error-label cleanup ladders that driver authors previously had to write manually in probe() and remove() functions. The mechanism is implemented compactly in drivers/base/devres.c, where each allocation stores a small header containing a release callback alongside the resource data. However, devres introduces its own risk: drivers that mix managed and manual cleanup can encounter subtle bugs, since devres runs after remove() returns rather than before it.