An almost catastrophic OpenZFS bug and the humans that made it(despairlabs.com)

    $ cat test.c
    
    #include <stdint.h>
    
    #define     DIV_ROUND_UP(n, d)  (((n) + (d) - 1) / (d))
    
    struct vdev;
    typedef struct vdev vdev_t;
    
    struct vdev
    {
        uint64_t     vdev_ashift;
        void        *vdev_tsd;
        vdev_t      *vdev_top;
    };
    
    struct vdev_raidz;
    typedef struct vdev_raidz vdev_raidz_t;
    
    struct vdev_raidz
    {
        int          vd_original_width;
        int          vd_physical_width;
        int          vd_nparity;
    };
    
    extern uint64_t vdev_raidz_get_logical_width(vdev_raidz_t *, uint64_t);
    
    static uint64_t
    vdev_raidz_asize_to_psize(vdev_t *vd, uint64_t asize, uint64_t txg)
    {
        vdev_raidz_t *vdrz = vd->vdev_tsd;
        uint64_t psize;
        uint64_t ashift = vd->vdev_top->vdev_ashift;
        uint64_t cols = vdrz->vd_original_width;
        uint64_t nparity = vdrz->vd_nparity;
    
        cols = vdev_raidz_get_logical_width(vdrz, txg);
    
        psize = (asize >> ashift);
        psize -= nparity * DIV_ROUND_UP(psize, cols);
        psize <<= ashift;
    
        return (asize);
    }



    $ gcc-14 -Wall -Wextra -Wpedantic -Wunused -Wunused-variable -Wunused-but-set-variable -c test.c -o test.o
    
    test.c:28:5: warning: ‘vdev_raidz_asize_to_psize’ defined but not used [-Wunused-function]
       28 |     vdev_raidz_asize_to_psize(vdev_t *vd, uint64_t asize, uint64_t txg)
          |     ^~~~~~~~~~~~~~~~~~~~~~~~~



    $ clang-19 -Weverything -c test.c -o test.o
    
    test.c:33:31: warning: implicit conversion changes signedness: 'int' to 'uint64_t' (aka 'unsigned long') [-Wsign-conversion]
       33 |         uint64_t cols = vdrz->vd_original_width;
          |                  ~~~~   ~~~~~~^~~~~~~~~~~~~~~~~
    
    test.c:34:34: warning: implicit conversion changes signedness: 'int' to 'uint64_t' (aka 'unsigned long') [-Wsign-conversion]
       34 |         uint64_t nparity = vdrz->vd_nparity;
          |                  ~~~~~~~   ~~~~~~^~~~~~~~~~
    
    test.c:28:5: warning: unused function 'vdev_raidz_asize_to_psize' [-Wunused-function]
       28 |     vdev_raidz_asize_to_psize(vdev_t *vd, uint64_t asize, uint64_t txg)
          |     ^~~~~~~~~~~~~~~~~~~~~~~~~
    
    3 warnings generated.