Hi Steven, On 2019/7/22 ????10:40, Steven Rostedt wrote: >>> and I'm not sure Al could accept __fdget conversion (I just wanted to give a example then...) >>> >>> Therefore, I tend to keep silence and just promote EROFS... some better ideas?... >>> >> Writing example conversion patches to demonstrate cleaner code >> and perhaps reduce LOC seems the best way. > Yes, I would be more interested in seeing patches that clean up the > code than just talking about it. > I guess that is related to me, though I didn't plan to promote a generic tagged pointer implementation in this series... I try to describe what erofs met and my own implementation, assume that we have 3 tagged pointers, a, b, c, and one potential user only (no need to ACCESS_ONCE). One way is #define A_MASK 1 #define B_MASK 1 #define C_MASK 3 /* now we have 3 mask there, A, B, C is simple, the real name could be long... */ void *a; void *b; void *c; /* and some pointers */ In order to decode the tag, we have to ((unsigned long)a & A_MASK) to decode the ptr, we have to ((unsigned long)a & ~A_MASK) In order to fold the tagged pointer... (void *)((unsigned long)a | tag) You can see the only meaning of these masks is the bitlength of tags, but there are many masks (or we have to do open-coded a & 3, if bitlength is changed, we have to fix them all)... therefore my approach is typedef tagptr1_t ta; /* tagptr type a with 1-bit tag */ typedef tagptr1_t tb; /* tagptr type b with 1-bit tag */ typedef tagptr2_t tc; /* tagptr type c with 2-bit tag */ and ta a; tb b; tc c; the type will represent its bitlength of tags and we can use ta, tb, tc to avoid masks or open-coded bitlength. In order to decode the tag, we can tagptr_unfold_tags(a) In order to decode the ptr, we can tagptr_unfold_ptr(a) In order to fold the tagged pointer... a = tagptr_fold(ta, ptr, tag) ACCESS_ONCE stuff is another thing... If my approach seems cleaner, we could move to include/linux later after EROFS stuffs is done... Or I could use a better tagptr approach later if any... Thanks, Gao XIang
