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Re: [Qemu-block] [PATCH 1/7] file-posix: Update open_flags in raw_set_pe


From: Kevin Wolf
Subject: Re: [Qemu-block] [PATCH 1/7] file-posix: Update open_flags in raw_set_perm()
Date: Wed, 8 May 2019 15:06:11 +0200
User-agent: Mutt/1.11.3 (2019-02-01)

Am 06.05.2019 um 21:47 hat Max Reitz geschrieben:
> raw_check_perm() + raw_set_perm() can change the flags associated with
> the current FD.  If so, we have to update BDRVRawState.open_flags
> accordingly.  Otherwise, we may keep reopening the FD even though the
> current one already has the correct flags.
> 
> Signed-off-by: Max Reitz <address@hidden>
> ---
>  block/file-posix.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/block/file-posix.c b/block/file-posix.c
> index 1cf4ee49eb..66b46ec0eb 100644
> --- a/block/file-posix.c
> +++ b/block/file-posix.c
> @@ -145,6 +145,7 @@ typedef struct BDRVRawState {
>      uint64_t locked_shared_perm;
>  
>      int perm_change_fd;
> +    int perm_change_flags;
>      BDRVReopenState *reopen_state;
>  
>  #ifdef CONFIG_XFS
> @@ -2762,6 +2763,7 @@ static int raw_check_perm(BlockDriverState *bs, 
> uint64_t perm, uint64_t shared,

Adding some context before this hunk:

    if (s->reopen_state) {
        /* We already have a new file descriptor to set permissions for */
        assert(s->reopen_state->perm == perm);
        assert(s->reopen_state->shared_perm == shared);
        rs = s->reopen_state->opaque;
        s->perm_change_fd = rs->fd;
    } else {
        /* We may need a new fd if auto-read-only switches the mode */
        ret = raw_reconfigure_getfd(bs, bs->open_flags, &open_flags, perm,
                                    false, errp);
        if (ret < 0) {
>              return ret;
>          } else if (ret != s->fd) {
>              s->perm_change_fd = ret;
> +            s->perm_change_flags = open_flags;
>          }
>      }

s->perm_change_flags is set in the else branch. According to the comment
in raw_set_perm(), not setting it in the then branch is actually correct
because .bdrv_reopen_commit will run first, so s->perm_change_flags
isn't accessed, but wouldn't it be nicer to have a valid value in it
anyway? Who knows where we'll add accesses later.

Kevin

> @@ -2800,6 +2802,7 @@ static void raw_set_perm(BlockDriverState *bs, uint64_t 
> perm, uint64_t shared)
>      if (s->perm_change_fd && s->fd != s->perm_change_fd) {
>          qemu_close(s->fd);
>          s->fd = s->perm_change_fd;
> +        s->open_flags = s->perm_change_flags;
>      }
>      s->perm_change_fd = 0;
>  
> -- 
> 2.20.1
> 



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