util/fifo8: Expose fifo8_pop_buf()

Extract fifo8_pop_buf() from hw/scsi/esp.c and expose
it as part of the <qemu/fifo8.h> API. This function takes
care of non-contiguous (wrapped) FIFO buffer (which is an
implementation detail).

Suggested-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Reviewed-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Message-Id: <20240722160745.67904-7-philmd@linaro.org>

hw/scsi/esp.c

@@ -197,39 +197,9 @@ static uint8_t esp_fifo_pop(ESPState *s)
     return val;
 }
 
-static uint32_t esp_fifo8_pop_buf(Fifo8 *fifo, uint8_t *dest, int maxlen)
-{
-    const uint8_t *buf;
-    uint32_t n, n2;
-    int len;
-
-    if (maxlen == 0) {
-        return 0;
-    }
-
-    len = maxlen;
-    buf = fifo8_pop_bufptr(fifo, len, &n);
-    if (dest) {
-        memcpy(dest, buf, n);
-    }
-
-    /* Add FIFO wraparound if needed */
-    len -= n;
-    len = MIN(len, fifo8_num_used(fifo));
-    if (len) {
-        buf = fifo8_pop_bufptr(fifo, len, &n2);
-        if (dest) {
-            memcpy(&dest[n], buf, n2);
-        }
-        n += n2;
-    }
-
-    return n;
-}
-
 static uint32_t esp_fifo_pop_buf(ESPState *s, uint8_t *dest, int maxlen)
 {
-    uint32_t len = esp_fifo8_pop_buf(&s->fifo, dest, maxlen);
+    uint32_t len = fifo8_pop_buf(&s->fifo, dest, maxlen);
 
     esp_update_drq(s);
     return len;
@@ -335,7 +305,7 @@ static void do_command_phase(ESPState *s)
     if (!cmdlen || !s->current_dev) {
         return;
     }
-    esp_fifo8_pop_buf(&s->cmdfifo, buf, cmdlen);
+    fifo8_pop_buf(&s->cmdfifo, buf, cmdlen);
 
     current_lun = scsi_device_find(&s->bus, 0, s->current_dev->id, s->lun);
     if (!current_lun) {
@@ -381,7 +351,7 @@ static void do_message_phase(ESPState *s)
     /* Ignore extended messages for now */
     if (s->cmdfifo_cdb_offset) {
         int len = MIN(s->cmdfifo_cdb_offset, fifo8_num_used(&s->cmdfifo));
-        esp_fifo8_pop_buf(&s->cmdfifo, NULL, len);
+        fifo8_pop_buf(&s->cmdfifo, NULL, len);
         s->cmdfifo_cdb_offset = 0;
     }
 }

include/qemu/fifo8.h

@@ -62,12 +62,28 @@ void fifo8_push_all(Fifo8 *fifo, const uint8_t *data, uint32_t num);
  */
 uint8_t fifo8_pop(Fifo8 *fifo);
 
+/**
+ * fifo8_pop_buf:
+ * @fifo: FIFO to pop from
+ * @dest: the buffer to write the data into (can be NULL)
+ * @destlen: size of @dest and maximum number of bytes to pop
+ *
+ * Pop a number of elements from the FIFO up to a maximum of @destlen.
+ * The popped data is copied into the @dest buffer.
+ * Care is taken when the data wraps around in the ring buffer.
+ *
+ * Returns: number of bytes popped.
+ */
+uint32_t fifo8_pop_buf(Fifo8 *fifo, uint8_t *dest, uint32_t destlen);
+
 /**
  * fifo8_pop_bufptr:
  * @fifo: FIFO to pop from
  * @max: maximum number of bytes to pop
  * @numptr: pointer filled with number of bytes returned (can be NULL)
  *
+ * New code should prefer to use fifo8_pop_buf() instead of fifo8_pop_bufptr().
+ *
  * Pop a number of elements from the FIFO up to a maximum of @max. The buffer
  * containing the popped data is returned. This buffer points directly into
  * the internal FIFO backing store and data (without checking for overflow!)

util/fifo8.c

@@ -102,6 +102,35 @@ const uint8_t *fifo8_pop_bufptr(Fifo8 *fifo, uint32_t max, uint32_t *numptr)
     return fifo8_peekpop_buf(fifo, max, numptr, true);
 }
 
+uint32_t fifo8_pop_buf(Fifo8 *fifo, uint8_t *dest, uint32_t destlen)
+{
+    const uint8_t *buf;
+    uint32_t n1, n2 = 0;
+    uint32_t len;
+
+    if (destlen == 0) {
+        return 0;
+    }
+
+    len = destlen;
+    buf = fifo8_pop_bufptr(fifo, len, &n1);
+    if (dest) {
+        memcpy(dest, buf, n1);
+    }
+
+    /* Add FIFO wraparound if needed */
+    len -= n1;
+    len = MIN(len, fifo8_num_used(fifo));
+    if (len) {
+        buf = fifo8_pop_bufptr(fifo, len, &n2);
+        if (dest) {
+            memcpy(&dest[n1], buf, n2);
+        }
+    }
+
+    return n1 + n2;
+}
+
 bool fifo8_is_empty(Fifo8 *fifo)
 {
     return (fifo->num == 0);