mirror of https://gitee.com/openkylin/qemu.git
qemu/queue.h: reimplement QTAILQ without pointer-to-pointers
QTAILQ is a doubly linked list, with a pointer-to-pointer to the last element from the head, and the previous element from each node. But if you squint enough, QTAILQ becomes a combination of a singly-linked forwards list, and another singly-linked list which goes backwards and is circular. This is the idea that lets QTAILQ implement reverse iteration: only, because the backwards list points inside the node, accessing the previous element needs to go two steps back and one forwards. What this patch does is implement it in these terms, without actually changing the in-memory layout at all. The coexistence of the two lists is realized by making QTAILQ_HEAD and QTAILQ_ENTRY unions of the forwards pointer and a generic QTailQLink node. Thq QTailQLink can walk the list in both directions; the union is needed so that the forwards pointer can have the correct type, as a sort of poor man's template. While there are other ways to get the same layout without a union, this one has the advantage of simpler operation in the debugger, because the fields tqh_first and tqe_next still exist as before the patch. Those fields are also used by scripts/qemugdb/mtree.py, so it's a good idea to preserve them. The advantage of the new representation is that the two-back-one-forward dance done by backwards accesses can be done all while operating on QTailQLinks. No casting to the head struct is needed anymore because, even though the QTailQLink's forward pointer is a void *, we can use typeof to recover the correct type. This patch only changes the implementation, not the interface. The next patch will remove the head struct name from the backwards visit macros. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini
parent
f95bb39cf1
commit
7274f01bb8
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@ -346,23 +346,28 @@ struct { \
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#define QSIMPLEQ_FIRST(head) ((head)->sqh_first)
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#define QSIMPLEQ_NEXT(elm, field) ((elm)->field.sqe_next)
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typedef struct QTailQLink {
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void *tql_next;
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struct QTailQLink *tql_prev;
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} QTailQLink;
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/*
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* Tail queue definitions.
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* Tail queue definitions. The union acts as a poor man template, as if
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* it were QTailQLink<type>.
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*/
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#define QTAILQ_HEAD(name, type) \
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struct name { \
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type *tqh_first; /* first element */ \
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type **tqh_last; /* addr of last next element */ \
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union name { \
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struct type *tqh_first; /* first element */ \
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QTailQLink tqh_circ; /* link for circular backwards list */ \
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}
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#define QTAILQ_HEAD_INITIALIZER(head) \
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{ NULL, &(head).tqh_first }
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{ .tqh_circ = { NULL, &(head).tqh_circ } }
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#define QTAILQ_ENTRY(type) \
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struct { \
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type *tqe_next; /* next element */ \
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type **tqe_prev; /* address of previous next element */ \
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union { \
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struct type *tqe_next; /* next element */ \
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QTailQLink tqe_circ; /* link for circular backwards list */ \
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}
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/*
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@ -370,51 +375,51 @@ struct { \
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*/
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#define QTAILQ_INIT(head) do { \
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(head)->tqh_first = NULL; \
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(head)->tqh_last = &(head)->tqh_first; \
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(head)->tqh_circ.tql_prev = &(head)->tqh_circ; \
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} while (/*CONSTCOND*/0)
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#define QTAILQ_INSERT_HEAD(head, elm, field) do { \
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if (((elm)->field.tqe_next = (head)->tqh_first) != NULL) \
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(head)->tqh_first->field.tqe_prev = \
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&(elm)->field.tqe_next; \
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(head)->tqh_first->field.tqe_circ.tql_prev = \
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&(elm)->field.tqe_circ; \
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else \
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(head)->tqh_last = &(elm)->field.tqe_next; \
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(head)->tqh_circ.tql_prev = &(elm)->field.tqe_circ; \
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(head)->tqh_first = (elm); \
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(elm)->field.tqe_prev = &(head)->tqh_first; \
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(elm)->field.tqe_circ.tql_prev = &(head)->tqh_circ; \
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} while (/*CONSTCOND*/0)
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#define QTAILQ_INSERT_TAIL(head, elm, field) do { \
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(elm)->field.tqe_next = NULL; \
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(elm)->field.tqe_prev = (head)->tqh_last; \
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*(head)->tqh_last = (elm); \
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(head)->tqh_last = &(elm)->field.tqe_next; \
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(elm)->field.tqe_circ.tql_prev = (head)->tqh_circ.tql_prev; \
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(head)->tqh_circ.tql_prev->tql_next = (elm); \
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(head)->tqh_circ.tql_prev = &(elm)->field.tqe_circ; \
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} while (/*CONSTCOND*/0)
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#define QTAILQ_INSERT_AFTER(head, listelm, elm, field) do { \
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if (((elm)->field.tqe_next = (listelm)->field.tqe_next) != NULL)\
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(elm)->field.tqe_next->field.tqe_prev = \
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&(elm)->field.tqe_next; \
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(elm)->field.tqe_next->field.tqe_circ.tql_prev = \
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&(elm)->field.tqe_circ; \
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else \
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(head)->tqh_last = &(elm)->field.tqe_next; \
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(head)->tqh_circ.tql_prev = &(elm)->field.tqe_circ; \
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(listelm)->field.tqe_next = (elm); \
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(elm)->field.tqe_prev = &(listelm)->field.tqe_next; \
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(elm)->field.tqe_circ.tql_prev = &(listelm)->field.tqe_circ; \
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} while (/*CONSTCOND*/0)
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#define QTAILQ_INSERT_BEFORE(listelm, elm, field) do { \
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(elm)->field.tqe_prev = (listelm)->field.tqe_prev; \
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(elm)->field.tqe_circ.tql_prev = (listelm)->field.tqe_circ.tql_prev; \
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(elm)->field.tqe_next = (listelm); \
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*(listelm)->field.tqe_prev = (elm); \
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(listelm)->field.tqe_prev = &(elm)->field.tqe_next; \
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(listelm)->field.tqe_circ.tql_prev->tql_next = (elm); \
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(listelm)->field.tqe_circ.tql_prev = &(elm)->field.tqe_circ; \
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} while (/*CONSTCOND*/0)
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#define QTAILQ_REMOVE(head, elm, field) do { \
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if (((elm)->field.tqe_next) != NULL) \
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(elm)->field.tqe_next->field.tqe_prev = \
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(elm)->field.tqe_prev; \
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(elm)->field.tqe_next->field.tqe_circ.tql_prev = \
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(elm)->field.tqe_circ.tql_prev; \
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else \
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(head)->tqh_last = (elm)->field.tqe_prev; \
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*(elm)->field.tqe_prev = (elm)->field.tqe_next; \
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(elm)->field.tqe_prev = NULL; \
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(head)->tqh_circ.tql_prev = (elm)->field.tqe_circ.tql_prev; \
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(elm)->field.tqe_circ.tql_prev->tql_next = (elm)->field.tqe_next; \
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(elm)->field.tqe_circ.tql_prev = NULL; \
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} while (/*CONSTCOND*/0)
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#define QTAILQ_FOREACH(var, head, field) \
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@ -428,13 +433,13 @@ struct { \
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(var) = (next_var))
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#define QTAILQ_FOREACH_REVERSE(var, head, headname, field) \
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for ((var) = (*(((struct headname *)((head)->tqh_last))->tqh_last)); \
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for ((var) = QTAILQ_LAST(head, headname); \
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(var); \
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(var) = (*(((struct headname *)((var)->field.tqe_prev))->tqh_last)))
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(var) = QTAILQ_PREV(var, headname, field))
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#define QTAILQ_FOREACH_REVERSE_SAFE(var, head, headname, field, prev_var) \
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for ((var) = (*(((struct headname *)((head)->tqh_last))->tqh_last)); \
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(var) && ((prev_var) = (*(((struct headname *)((var)->field.tqe_prev))->tqh_last)), 1); \
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for ((var) = QTAILQ_LAST(head, headname); \
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(var) && ((prev_var) = QTAILQ_PREV(var, headname, field)); \
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(var) = (prev_var))
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/*
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@ -443,71 +448,49 @@ struct { \
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#define QTAILQ_EMPTY(head) ((head)->tqh_first == NULL)
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#define QTAILQ_FIRST(head) ((head)->tqh_first)
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#define QTAILQ_NEXT(elm, field) ((elm)->field.tqe_next)
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#define QTAILQ_IN_USE(elm, field) ((elm)->field.tqe_prev != NULL)
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#define QTAILQ_IN_USE(elm, field) ((elm)->field.tqe_circ.tql_prev != NULL)
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#define QTAILQ_LINK_PREV(link) \
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((link).tql_prev->tql_prev->tql_next)
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#define QTAILQ_LAST(head, headname) \
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(*(((struct headname *)((head)->tqh_last))->tqh_last))
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((typeof((head)->tqh_first)) QTAILQ_LINK_PREV((head)->tqh_circ))
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#define QTAILQ_PREV(elm, headname, field) \
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(*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
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((typeof((elm)->field.tqe_next)) QTAILQ_LINK_PREV((elm)->field.tqe_circ))
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#define field_at_offset(base, offset, type) \
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((type) (((char *) (base)) + (offset)))
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typedef struct DUMMY_Q_ENTRY DUMMY_Q_ENTRY;
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typedef struct DUMMY_Q DUMMY_Q;
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struct DUMMY_Q_ENTRY {
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QTAILQ_ENTRY(DUMMY_Q_ENTRY) next;
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};
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struct DUMMY_Q {
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QTAILQ_HEAD(DUMMY_Q_HEAD, DUMMY_Q_ENTRY) head;
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};
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#define dummy_q ((DUMMY_Q *) 0)
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#define dummy_qe ((DUMMY_Q_ENTRY *) 0)
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((type *) (((char *) (base)) + (offset)))
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/*
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* Offsets of layout of a tail queue head.
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*/
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#define QTAILQ_FIRST_OFFSET (offsetof(typeof(dummy_q->head), tqh_first))
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#define QTAILQ_LAST_OFFSET (offsetof(typeof(dummy_q->head), tqh_last))
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/*
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* Raw access of elements of a tail queue
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* Raw access of elements of a tail queue head. Offsets are all zero
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* because it's a union.
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*/
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#define QTAILQ_RAW_FIRST(head) \
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(*field_at_offset(head, QTAILQ_FIRST_OFFSET, void **))
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#define QTAILQ_RAW_TQH_LAST(head) \
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(*field_at_offset(head, QTAILQ_LAST_OFFSET, void ***))
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/*
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* Offsets of layout of a tail queue element.
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*/
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#define QTAILQ_NEXT_OFFSET (offsetof(typeof(dummy_qe->next), tqe_next))
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#define QTAILQ_PREV_OFFSET (offsetof(typeof(dummy_qe->next), tqe_prev))
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field_at_offset(head, 0, void *)
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#define QTAILQ_RAW_TQH_CIRC(head) \
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field_at_offset(head, 0, QTailQLink)
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/*
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* Raw access of elements of a tail entry
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*/
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#define QTAILQ_RAW_NEXT(elm, entry) \
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(*field_at_offset(elm, entry + QTAILQ_NEXT_OFFSET, void **))
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#define QTAILQ_RAW_TQE_PREV(elm, entry) \
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(*field_at_offset(elm, entry + QTAILQ_PREV_OFFSET, void ***))
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field_at_offset(elm, entry, void *)
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#define QTAILQ_RAW_TQE_CIRC(elm, entry) \
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field_at_offset(elm, entry, QTailQLink)
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/*
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* Tail queue tranversal using pointer arithmetic.
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* Tail queue traversal using pointer arithmetic.
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*/
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#define QTAILQ_RAW_FOREACH(elm, head, entry) \
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for ((elm) = QTAILQ_RAW_FIRST(head); \
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for ((elm) = *QTAILQ_RAW_FIRST(head); \
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(elm); \
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(elm) = QTAILQ_RAW_NEXT(elm, entry))
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(elm) = *QTAILQ_RAW_NEXT(elm, entry))
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/*
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* Tail queue insertion using pointer arithmetic.
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*/
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#define QTAILQ_RAW_INSERT_TAIL(head, elm, entry) do { \
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QTAILQ_RAW_NEXT(elm, entry) = NULL; \
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QTAILQ_RAW_TQE_PREV(elm, entry) = QTAILQ_RAW_TQH_LAST(head); \
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*QTAILQ_RAW_TQH_LAST(head) = (elm); \
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QTAILQ_RAW_TQH_LAST(head) = &QTAILQ_RAW_NEXT(elm, entry); \
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*QTAILQ_RAW_NEXT(elm, entry) = NULL; \
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QTAILQ_RAW_TQE_CIRC(elm, entry)->tql_prev = QTAILQ_RAW_TQH_CIRC(head)->tql_prev; \
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QTAILQ_RAW_TQH_CIRC(head)->tql_prev->tql_next = (elm); \
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QTAILQ_RAW_TQH_CIRC(head)->tql_prev = QTAILQ_RAW_TQE_CIRC(elm, entry); \
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} while (/*CONSTCOND*/0)
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#endif /* QEMU_SYS_QUEUE_H */
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@ -206,47 +206,50 @@ extern "C" {
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#define QTAILQ_INSERT_HEAD_RCU(head, elm, field) do { \
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(elm)->field.tqe_next = (head)->tqh_first; \
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if ((elm)->field.tqe_next != NULL) { \
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(head)->tqh_first->field.tqe_prev = &(elm)->field.tqe_next; \
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(head)->tqh_first->field.tqe_circ.tql_prev = \
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&(elm)->field.tqe_circ; \
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} else { \
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(head)->tqh_last = &(elm)->field.tqe_next; \
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(head)->tqh_circ.tql_prev = &(elm)->field.tqe_circ; \
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} \
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atomic_rcu_set(&(head)->tqh_first, (elm)); \
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(elm)->field.tqe_prev = &(head)->tqh_first; \
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(elm)->field.tqe_circ.tql_prev = &(head)->tqh_circ; \
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} while (/*CONSTCOND*/0)
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#define QTAILQ_INSERT_TAIL_RCU(head, elm, field) do { \
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(elm)->field.tqe_next = NULL; \
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(elm)->field.tqe_prev = (head)->tqh_last; \
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atomic_rcu_set((head)->tqh_last, (elm)); \
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(head)->tqh_last = &(elm)->field.tqe_next; \
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(elm)->field.tqe_circ.tql_prev = (head)->tqh_circ.tql_prev; \
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atomic_rcu_set(&(head)->tqh_circ.tql_prev->tql_next, (elm)); \
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(head)->tqh_circ.tql_prev = &(elm)->field.tqe_circ; \
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} while (/*CONSTCOND*/0)
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#define QTAILQ_INSERT_AFTER_RCU(head, listelm, elm, field) do { \
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(elm)->field.tqe_next = (listelm)->field.tqe_next; \
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if ((elm)->field.tqe_next != NULL) { \
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(elm)->field.tqe_next->field.tqe_prev = &(elm)->field.tqe_next; \
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(elm)->field.tqe_next->field.tqe_circ.tql_prev = \
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&(elm)->field.tqe_circ; \
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} else { \
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(head)->tqh_last = &(elm)->field.tqe_next; \
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(head)->tqh_circ.tql_prev = &(elm)->field.tqe_circ; \
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} \
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atomic_rcu_set(&(listelm)->field.tqe_next, (elm)); \
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(elm)->field.tqe_prev = &(listelm)->field.tqe_next; \
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(elm)->field.tqe_circ.tql_prev = &(listelm)->field.tqe_circ; \
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} while (/*CONSTCOND*/0)
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#define QTAILQ_INSERT_BEFORE_RCU(listelm, elm, field) do { \
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(elm)->field.tqe_prev = (listelm)->field.tqe_prev; \
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(elm)->field.tqe_circ.tql_prev = (listelm)->field.tqe_circ.tql_prev; \
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(elm)->field.tqe_next = (listelm); \
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atomic_rcu_set((listelm)->field.tqe_prev, (elm)); \
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(listelm)->field.tqe_prev = &(elm)->field.tqe_next; \
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} while (/*CONSTCOND*/0)
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atomic_rcu_set(&(listelm)->field.tqe_circ.tql_prev->tql_next, (elm)); \
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(listelm)->field.tqe_circ.tql_prev = &(elm)->field.tqe_circ; \
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} while (/*CONSTCOND*/0)
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#define QTAILQ_REMOVE_RCU(head, elm, field) do { \
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if (((elm)->field.tqe_next) != NULL) { \
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(elm)->field.tqe_next->field.tqe_prev = (elm)->field.tqe_prev; \
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(elm)->field.tqe_next->field.tqe_circ.tql_prev = \
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(elm)->field.tqe_circ.tql_prev; \
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} else { \
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(head)->tqh_last = (elm)->field.tqe_prev; \
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(head)->tqh_circ.tql_prev = (elm)->field.tqe_circ.tql_prev; \
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} \
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atomic_set((elm)->field.tqe_prev, (elm)->field.tqe_next); \
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(elm)->field.tqe_prev = NULL; \
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atomic_set(&(elm)->field.tqe_circ.tql_prev->tql_next, (elm)->field.tqe_next); \
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(elm)->field.tqe_circ.tql_prev = NULL; \
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} while (/*CONSTCOND*/0)
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#define QTAILQ_FOREACH_RCU(var, head, field) \
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@ -93,18 +93,18 @@ struct { \
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* Tail queue definitions.
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*/
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#define QTAILQ_HEAD(name, type) \
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struct name { \
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type *tqh_first; /* first element */ \
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type **tqh_last; /* addr of last next element */ \
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union name { \
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struct type *tqh_first; /* first element */ \
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QTailQLink tqh_circ; /* link for last element */ \
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}
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#define QTAILQ_HEAD_INITIALIZER(head) \
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{ NULL, &(head).tqh_first }
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{ .tqh_circ = { NULL, &(head).tqh_circ } }
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#define QTAILQ_ENTRY(type) \
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struct { \
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type *tqe_next; /* next element */ \
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type **tqe_prev; /* address of previous next element */ \
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union { \
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struct type *tqe_next; /* next element */ \
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QTailQLink tqe_circ; /* link for prev element */ \
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}
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/* From glib */
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