[Qemu-block] [PULL for-2.8 08/13] block/curl: Drop TFTP "support"

[Jeff Cody]

From: Max Reitz <address@hidden>

Because TFTP does not support byte ranges, it was never usable with our
curl block driver. Since apparently nobody has ever complained loudly
enough for someone to take care of the issue until now, it seems
reasonable to assume that nobody has ever actually used it.

Therefore, it should be safe to just drop it from curl's protocol list.

[Jeff Cody: Below is additional summary pulled, with some rewording,
            from followup emails between Max and Markus, to explain what
            worked and what didn't]

TFTP would sometimes work, to a limited extent, for images <= the curl
"readahead" size, so long as reads started at offset zero.  By default,
that readahead size is 256KB.

Reads starting at a non-zero offset would also have returned data from a
zero offset.  It can become more complicated still, with mixed reads at
zero offset and non-zero offsets, due to data buffering.

In short, TFTP could only have worked before in very specific scenarios
with unrealistic expectations and constraints.

Signed-off-by: Max Reitz <address@hidden>
Reviewed-by: Kevin Wolf <address@hidden>
Reviewed-by: Jeff Cody <address@hidden>
Message-id: address@hidden
Signed-off-by: Jeff Cody <address@hidden>
---
 block/curl.c          | 20 +-------------------
 docs/qmp-commands.txt |  2 +-
 qapi/block-core.json  |  7 +++----
 qemu-options.hx       |  6 +++---
 4 files changed, 8 insertions(+), 27 deletions(-)

diff --git a/block/curl.c b/block/curl.c
index e5eaa7b..ba8adae 100644
--- a/block/curl.c
+++ b/block/curl.c
@@ -68,8 +68,7 @@ static CURLMcode __curl_multi_socket_action(CURLM 
*multi_handle,
 #endif
 
 #define PROTOCOLS (CURLPROTO_HTTP | CURLPROTO_HTTPS | \
-                   CURLPROTO_FTP | CURLPROTO_FTPS | \
-                   CURLPROTO_TFTP)
+                   CURLPROTO_FTP | CURLPROTO_FTPS)
 
 #define CURL_NUM_STATES 8
 #define CURL_NUM_ACB    8
@@ -886,29 +885,12 @@ static BlockDriver bdrv_ftps = {
     .bdrv_attach_aio_context    = curl_attach_aio_context,
 };
 
-static BlockDriver bdrv_tftp = {
-    .format_name                = "tftp",
-    .protocol_name              = "tftp",
-
-    .instance_size              = sizeof(BDRVCURLState),
-    .bdrv_parse_filename        = curl_parse_filename,
-    .bdrv_file_open             = curl_open,
-    .bdrv_close                 = curl_close,
-    .bdrv_getlength             = curl_getlength,
-
-    .bdrv_aio_readv             = curl_aio_readv,
-
-    .bdrv_detach_aio_context    = curl_detach_aio_context,
-    .bdrv_attach_aio_context    = curl_attach_aio_context,
-};
-
 static void curl_block_init(void)
 {
     bdrv_register(&bdrv_http);
     bdrv_register(&bdrv_https);
     bdrv_register(&bdrv_ftp);
     bdrv_register(&bdrv_ftps);
-    bdrv_register(&bdrv_tftp);
 }
 
 block_init(curl_block_init);
diff --git a/docs/qmp-commands.txt b/docs/qmp-commands.txt
index 6afa872..abf210a 100644
--- a/docs/qmp-commands.txt
+++ b/docs/qmp-commands.txt
@@ -1803,7 +1803,7 @@ Each json-object contain the following:
                                 "file", "file", "ftp", "ftps", "host_cdrom",
                                 "host_device", "http", "https",
                                 "nbd", "parallels", "qcow", "qcow2", "raw",
-                                "tftp", "vdi", "vmdk", "vpc", "vvfat"
+                                "vdi", "vmdk", "vpc", "vvfat"
          - "backing_file": backing file name (json-string, optional)
          - "backing_file_depth": number of files in the backing file chain 
(json-int)
          - "encrypted": true if encrypted, false otherwise (json-bool)
diff --git a/qapi/block-core.json b/qapi/block-core.json
index bcd3b9e..c29bef7 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -243,12 +243,12 @@
 #       0.14.0 this can be: 'blkdebug', 'bochs', 'cloop', 'cow', 'dmg',
 #       'file', 'file', 'ftp', 'ftps', 'host_cdrom', 'host_device',
 #       'http', 'https', 'luks', 'nbd', 'parallels', 'qcow',
-#       'qcow2', 'raw', 'tftp', 'vdi', 'vmdk', 'vpc', 'vvfat'
+#       'qcow2', 'raw', 'vdi', 'vmdk', 'vpc', 'vvfat'
 #       2.2: 'archipelago' added, 'cow' dropped
 #       2.3: 'host_floppy' deprecated
 #       2.5: 'host_floppy' dropped
 #       2.6: 'luks' added
-#       2.8: 'replication' added
+#       2.8: 'replication' added, 'tftp' dropped
 #
 # @backing_file: #optional the name of the backing file (for copy-on-write)
 #
@@ -1723,7 +1723,7 @@
             'dmg', 'file', 'ftp', 'ftps', 'gluster', 'host_cdrom',
             'host_device', 'http', 'https', 'luks', 'nbd', 'nfs', 'null-aio',
             'null-co', 'parallels', 'qcow', 'qcow2', 'qed', 'quorum', 'raw',
-            'replication', 'ssh', 'tftp', 'vdi', 'vhdx', 'vmdk', 'vpc',
+            'replication', 'ssh', 'vdi', 'vhdx', 'vmdk', 'vpc',
             'vvfat' ] }
 
 ##
@@ -2410,7 +2410,6 @@
       'replication':'BlockdevOptionsReplication',
 # TODO sheepdog: Wait for structured options
       'ssh':        'BlockdevOptionsSsh',
-      'tftp':       'BlockdevOptionsCurl',
       'vdi':        'BlockdevOptionsGenericFormat',
       'vhdx':       'BlockdevOptionsGenericFormat',
       'vmdk':       'BlockdevOptionsGenericCOWFormat',
diff --git a/qemu-options.hx b/qemu-options.hx
index 4536e18..4a5b29f 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -2606,8 +2606,8 @@ qemu-system-x86_64 --drive 
file=gluster://192.0.2.1/testvol/a.img
 
 See also @url{http://www.gluster.org}.
 
address@hidden HTTP/HTTPS/FTP/FTPS/TFTP
-QEMU supports read-only access to files accessed over http(s), ftp(s) and tftp.
address@hidden HTTP/HTTPS/FTP/FTPS
+QEMU supports read-only access to files accessed over http(s) and ftp(s).
 
 Syntax using a single filename:
 @example
@@ -2617,7 +2617,7 @@ Syntax using a single filename:
 where:
 @table @option
 @item protocol
-'http', 'https', 'ftp', 'ftps', or 'tftp'.
+'http', 'https', 'ftp', or 'ftps'.
 
 @item username
 Optional username for authentication to the remote server.
-- 
2.7.4