block/block-backend.c

   1 /*
   2  * QEMU Block backends
   3  *
   4  * Copyright (C) 2014 Red Hat, Inc.
   5  *
   6  * Authors:
   7  *  Markus Armbruster <armbru@redhat.com>,
   8  *
   9  * This work is licensed under the terms of the GNU LGPL, version 2.1
  10  * or later.  See the COPYING.LIB file in the top-level directory.
  11  */
  12
  13 #include "sysemu/block-backend.h"
  14 #include "block/block_int.h"
  15
  16 struct BlockBackend {
  17     char *name;
  18     int refcnt;
  19     QTAILQ_ENTRY(BlockBackend) link; /* for blk_backends */
  20 };
  21
  22 /* All the BlockBackends */
  23 static QTAILQ_HEAD(, BlockBackend) blk_backends =
  24     QTAILQ_HEAD_INITIALIZER(blk_backends);
  25
  26 /*
  27  * Create a new BlockBackend with @name, with a reference count of one.
  28  * @name must not be null or empty.
  29  * Fail if a BlockBackend with this name already exists.
  30  * Store an error through @errp on failure, unless it's null.
  31  * Return the new BlockBackend on success, null on failure.
  32  */
  33 BlockBackend *blk_new(const char *name, Error **errp)
  34 {
  35     BlockBackend *blk;
  36
  37     assert(name && name[0]);
  38     if (blk_by_name(name)) {
  39         error_setg(errp, "Device with id '%s' already exists", name);
  40         return NULL;
  41     }
  42
  43     blk = g_new0(BlockBackend, 1);
  44     blk->name = g_strdup(name);
  45     blk->refcnt = 1;
  46     QTAILQ_INSERT_TAIL(&blk_backends, blk, link);
  47     return blk;
  48 }
  49
  50 static void blk_delete(BlockBackend *blk)
  51 {
  52     assert(!blk->refcnt);
  53     QTAILQ_REMOVE(&blk_backends, blk, link);
  54     g_free(blk->name);
  55     g_free(blk);
  56 }
  57
  58 /*
  59  * Increment @blk's reference count.
  60  * @blk must not be null.
  61  */
  62 void blk_ref(BlockBackend *blk)
  63 {
  64     blk->refcnt++;
  65 }
  66
  67 /*
  68  * Decrement @blk's reference count.
  69  * If this drops it to zero, destroy @blk.
  70  * For convenience, do nothing if @blk is null.
  71  */
  72 void blk_unref(BlockBackend *blk)
  73 {
  74     if (blk) {
  75         assert(blk->refcnt > 0);
  76         if (!--blk->refcnt) {
  77             blk_delete(blk);
  78         }
  79     }
  80 }
  81
  82 /*
  83  * Return the BlockBackend after @blk.
  84  * If @blk is null, return the first one.
  85  * Else, return @blk's next sibling, which may be null.
  86  *
  87  * To iterate over all BlockBackends, do
  88  * for (blk = blk_next(NULL); blk; blk = blk_next(blk)) {
  89  *     ...
  90  * }
  91  */
  92 BlockBackend *blk_next(BlockBackend *blk)
  93 {
  94     return blk ? QTAILQ_NEXT(blk, link) : QTAILQ_FIRST(&blk_backends);
  95 }
  96
  97 /*
  98  * Return @blk's name, a non-null, non-empty string.
  99  */
 100 const char *blk_name(BlockBackend *blk)
 101 {
 102     return blk->name;
 103 }
 104
 105 /*
 106  * Return the BlockBackend with name @name if it exists, else null.
 107  * @name must not be null.
 108  */
 109 BlockBackend *blk_by_name(const char *name)
 110 {
 111     BlockBackend *blk;
 112
 113     assert(name);
 114     QTAILQ_FOREACH(blk, &blk_backends, link) {
 115         if (!strcmp(name, blk->name)) {
 116             return blk;
 117         }
 118     }
 119     return NULL;
 120 }