Re: [Qemu-block] [Qemu-devel] [PATCH 2/3] block/ssh: Make ssh_grow_file() blocking

[Max Reitz]

On 2018-02-14 22:11, Eric Blake wrote:
> On 02/14/2018 02:49 PM, Max Reitz wrote:
>> At runtime (that is, during a future ssh_truncate()), the SSH session is
>> non-blocking.  However, ssh_truncate() (or rather, bdrv_truncate() in
>> general) is not a coroutine, so this resize operation needs to block.
>>
>> For ssh_create(), that is fine, too; the session is never set to
>> non-blocking anyway.
>>
>> Signed-off-by: Max Reitz 
>> ---
>>   block/ssh.c | 7 +++
>>   1 file changed, 7 insertions(+)
>>
>> diff --git a/block/ssh.c b/block/ssh.c
>> index 964e55f7fe..ff8576f21e 100644
>> --- a/block/ssh.c
>> +++ b/block/ssh.c
>> @@ -803,17 +803,24 @@ static int ssh_file_open(BlockDriverState *bs,
>> QDict *options, int bdrv_flags,
>>   return ret;
>>   }
>>   +/* Note: This is a blocking operation */
>>   static int ssh_grow_file(BDRVSSHState *s, int64_t offset, Error **errp)
>>   {
>>   ssize_t ret;
>>   char c[1] = { '\0' };
>> +    int was_blocking = libssh2_session_get_blocking(s->session);
>>     /* offset must be strictly greater than the current size so we do
>>    * not overwrite anything */
>>   assert(offset > 0 && offset > s->attrs.filesize);
>>   +    libssh2_session_set_blocking(s->session, 1);
>> +
>>   libssh2_sftp_seek64(s->sftp_handle, offset - 1);
>>   ret = libssh2_sftp_write(s->sftp_handle, c, 1);
>> +
>> +    libssh2_session_set_blocking(s->session, was_blocking);
> 
> Is it worth skipping the two libssh2_session_set_blocking() calls if
> was_blocking is 1?  But that's a micro-optimization that probably won't
> be noticeable, so I'm also fine with unconditional.

I was hoping libssh2 is clever enough for that itself. :-)

> Reviewed-by: Eric Blake 

Thanks!

Max



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Re: [Qemu-block] [Qemu-devel] [PATCH 2/3] block/ssh: Make ssh_grow_file() blocking

[Eric Blake]

On 02/14/2018 02:49 PM, Max Reitz wrote:

At runtime (that is, during a future ssh_truncate()), the SSH session is
non-blocking.  However, ssh_truncate() (or rather, bdrv_truncate() in
general) is not a coroutine, so this resize operation needs to block.

For ssh_create(), that is fine, too; the session is never set to
non-blocking anyway.

Signed-off-by: Max Reitz 
---
  block/ssh.c | 7 +++
  1 file changed, 7 insertions(+)

diff --git a/block/ssh.c b/block/ssh.c
index 964e55f7fe..ff8576f21e 100644
--- a/block/ssh.c
+++ b/block/ssh.c
@@ -803,17 +803,24 @@ static int ssh_file_open(BlockDriverState *bs, QDict 
*options, int bdrv_flags,
  return ret;
  }
  
+/* Note: This is a blocking operation */

  static int ssh_grow_file(BDRVSSHState *s, int64_t offset, Error **errp)
  {
  ssize_t ret;
  char c[1] = { '\0' };
+int was_blocking = libssh2_session_get_blocking(s->session);
  
  /* offset must be strictly greater than the current size so we do

   * not overwrite anything */
  assert(offset > 0 && offset > s->attrs.filesize);
  
+libssh2_session_set_blocking(s->session, 1);

+
  libssh2_sftp_seek64(s->sftp_handle, offset - 1);
  ret = libssh2_sftp_write(s->sftp_handle, c, 1);
+
+libssh2_session_set_blocking(s->session, was_blocking);


Is it worth skipping the two libssh2_session_set_blocking() calls if 
was_blocking is 1?  But that's a micro-optimization that probably won't 
be noticeable, so I'm also fine with unconditional.


Reviewed-by: Eric Blake 

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.   +1-919-301-3266
Virtualization:  qemu.org | libvirt.org