Re: [Qemu-devel] [PATCH 1/1] block/file-posix.c: fix not reopened lock file descriptor

[Kevin Wolf <kwolf@redhat.com>]

[ Cc: qemu-block ]

Am 22.03.2018 um 18:20 hat Dion Bosschieter geschrieben:
> In commit 244a5668106297378391b768e7288eb157616f64 another
> file descriptor to BDRVRawState is added. When we try to issue the
> reopen command only s->fd is reopened; lock_fd could still hold an old
> file descriptor "possibly" pointing to another file.
> 
> - change raw_reopen_prepare so it checks use_lock from BDRVRawState and
> tries to reopen lock_fd accordingly
> - change raw_reopen_commit so it closes the old lock_fd on use_lock
> 
> Signed-off-by: Dion Bosschieter <dionbosschieter@gmail.com>

bdrv_reopen() is not meant for opening a different file, it is meant to
change the flags and options of the same file. Do you have a use case
where you would actually need to switch to a different file?

As far as I know, lock_fd was specifically introduced _because_ it stays
the same across reopen, so we don't need a racy release/reacquire pair.
Fam (CCed) should know more.

In any case, doesn't your patch drop all the locks without reacquiring
them on the new lock_fd?

Kevin

>  block/file-posix.c | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 
> diff --git a/block/file-posix.c b/block/file-posix.c
> index d7fb772c14..16d83fc49e 100644
> --- a/block/file-posix.c
> +++ b/block/file-posix.c
> @@ -167,6 +167,7 @@ typedef struct BDRVRawState {
>  
>  typedef struct BDRVRawReopenState {
>      int fd;
> +    int lock_fd;
>      int open_flags;
>  } BDRVRawReopenState;
>  
> @@ -795,6 +796,7 @@ static int raw_reopen_prepare(BDRVReopenState *state,
>      raw_parse_flags(state->flags, &rs->open_flags);
>  
>      rs->fd = -1;
> +    rs->lock_fd = -1;
>  
>      int fcntl_flags = O_APPEND | O_NONBLOCK;
>  #ifdef O_NOATIME
> @@ -820,6 +822,17 @@ static int raw_reopen_prepare(BDRVReopenState *state,
>                  rs->fd = -1;
>              }
>          }
> +
> +        if (s->use_lock) {
> +            rs->lock_fd = qemu_dup(s->lock_fd);
> +            if (rs->lock_fd >= 0) {
> +                ret = fcntl_setfl(rs->lock_fd, rs->open_flags);
> +                if (ret) {
> +                    qemu_close(rs->lock_fd);
> +                    rs->lock_fd = -1;
> +                }
> +            }
> +        }
>      }
>  
>      /* If we cannot use fcntl, or fcntl failed, fall back to qemu_open() */
> @@ -835,6 +848,14 @@ static int raw_reopen_prepare(BDRVReopenState *state,
>                  error_setg_errno(errp, errno, "Could not reopen file");
>                  ret = -1;
>              }
> +
> +            if (s->use_lock) {
> +                rs->lock_fd = qemu_open(normalized_filename, rs->open_flags);
> +                if (rs->lock_fd == -1) {
> +                    error_setg_errno(errp, errno, "Could not reopen file for locking");
> +                    ret = -1;
> +                }
> +            }
>          }
>      }
>  
> @@ -861,7 +882,11 @@ static void raw_reopen_commit(BDRVReopenState *state)
>      s->open_flags = rs->open_flags;
>  
>      qemu_close(s->fd);
> +    if (s->use_lock) {
> +        qemu_close(s->lock_fd);
> +    }
>      s->fd = rs->fd;
> +    s->lock_fd = rs->lock_fd;
>  
>      g_free(state->opaque);
>      state->opaque = NULL;
> -- 
> 2.14.2
>