block: Cater to iscsi with non-power-of-2 discard

[mirror_qemu.git] / include / block / block_int.h

diff --git a/include/block/block_int.h b/include/block/block_int.h
index 1fe0fd9ff61b1dbbfce633293b0178fab10f6de0..47665be81e2392810a3bc8eff79b7747302a663a 100644 (file)
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -330,36 +330,39 @@ typedef struct BlockLimits {
      * otherwise. */
     uint32_t request_alignment;
 
-    /* maximum number of bytes that can be discarded at once (since it
-     * is signed, it must be < 2G, if set), should be multiple of
+    /* Maximum number of bytes that can be discarded at once (since it
+     * is signed, it must be < 2G, if set). Must be multiple of
      * pdiscard_alignment, but need not be power of 2. May be 0 if no
      * inherent 32-bit limit */
     int32_t max_pdiscard;
 
-    /* optimal alignment for discard requests in bytes, must be power
-     * of 2, less than max_pdiscard if that is set, and multiple of
-     * bl.request_alignment. May be 0 if bl.request_alignment is good
-     * enough */
+    /* Optimal alignment for discard requests in bytes. A power of 2
+     * is best but not mandatory.  Must be a multiple of
+     * bl.request_alignment, and must be less than max_pdiscard if
+     * that is set. May be 0 if bl.request_alignment is good enough */
     uint32_t pdiscard_alignment;
 
-    /* maximum number of bytes that can zeroized at once (since it is
-     * signed, it must be < 2G, if set), should be multiple of
+    /* Maximum number of bytes that can zeroized at once (since it is
+     * signed, it must be < 2G, if set). Must be multiple of
      * pwrite_zeroes_alignment. May be 0 if no inherent 32-bit limit */
     int32_t max_pwrite_zeroes;
 
-    /* optimal alignment for write zeroes requests in bytes, must be
-     * power of 2, less than max_pwrite_zeroes if that is set, and
-     * multiple of bl.request_alignment. May be 0 if
-     * bl.request_alignment is good enough */
+    /* Optimal alignment for write zeroes requests in bytes. A power
+     * of 2 is best but not mandatory.  Must be a multiple of
+     * bl.request_alignment, and must be less than max_pwrite_zeroes
+     * if that is set. May be 0 if bl.request_alignment is good
+     * enough */
     uint32_t pwrite_zeroes_alignment;
 
-    /* optimal transfer length in bytes (must be power of 2, and
-     * multiple of bl.request_alignment), or 0 if no preferred size */
+    /* Optimal transfer length in bytes.  A power of 2 is best but not
+     * mandatory.  Must be a multiple of bl.request_alignment, or 0 if
+     * no preferred size */
     uint32_t opt_transfer;
 
-    /* maximal transfer length in bytes (need not be power of 2, but
-     * should be multiple of opt_transfer), or 0 for no 32-bit limit.
-     * For now, anything larger than INT_MAX is clamped down. */
+    /* Maximal transfer length in bytes.  Need not be power of 2, but
+     * must be multiple of opt_transfer and bl.request_alignment, or 0
+     * for no 32-bit limit.  For now, anything larger than INT_MAX is
+     * clamped down. */
     uint32_t max_transfer;
 
     /* memory alignment, in bytes so that no bounce buffer is needed */