Re: [PATCH v3 2/2] block/rbd: Add an escape-aware strchr helper

From: Stefano Garzarella <sgarzare@redhat.com>
To: Connor Kuehl <ckuehl@redhat.com>
Cc: kwolf@redhat.com, qemu-devel@nongnu.org, qemu-block@nongnu.org,
	mreitz@redhat.com
Subject: Re: [PATCH v3 2/2] block/rbd: Add an escape-aware strchr helper
Date: Wed, 21 Apr 2021 13:04:54 +0200	[thread overview]
Message-ID: <20210421110454.6jcig7ujr25my2xw@steredhat> (raw)
In-Reply-To: <20210409143854.138177-3-ckuehl@redhat.com>

On Fri, Apr 09, 2021 at 09:38:54AM -0500, Connor Kuehl wrote:
>Sometimes the parser needs to further split a token it has collected
>from the token input stream. Right now, it does a cursory check to see
>if the relevant characters appear in the token to determine if it should
>break it down further.
>
>However, qemu_rbd_next_tok() will escape characters as it removes tokens
>from the token stream and plain strchr() won't. This can make the
>initial strchr() check slightly misleading since it implies
>qemu_rbd_next_tok() will find the token and split on it, except the
>reality is that qemu_rbd_next_tok() will pass over it if it is escaped.
>
>Use a custom strchr to avoid mixing escaped and unescaped string
>operations.
>
>Reported-by: Han Han <hhan@redhat.com>
>Fixes: https://bugzilla.redhat.com/1873913
>Signed-off-by: Connor Kuehl <ckuehl@redhat.com>
>---
>  v2 -> v3:
>    * Update qemu_rbd_strchr to only skip if there's a delimiter AND the
>      next character is not the NUL terminator
>
> block/rbd.c                | 20 ++++++++++++++++++--
> tests/qemu-iotests/231     |  4 ++++
> tests/qemu-iotests/231.out |  3 +++
> 3 files changed, 25 insertions(+), 2 deletions(-)
>
>diff --git a/block/rbd.c b/block/rbd.c
>index 9071a00e3f..291e3f09e1 100644
>--- a/block/rbd.c
>+++ b/block/rbd.c
>@@ -134,6 +134,22 @@ static char *qemu_rbd_next_tok(char *src, char delim, char **p)
>     return src;
> }
>
>+static char *qemu_rbd_strchr(char *src, char delim)
>+{
>+    char *p;
>+
>+    for (p = src; *p; ++p) {
>+        if (*p == delim) {
>+            return p;
>+        }
>+        if (*p == '\\' && p[1] != '\0') {
>+            ++p;
>+        }
>+    }
>+
>+    return NULL;
>+}
>+

IIUC this is similar to the code used in qemu_rbd_next_tok().
To avoid code duplication can we use this new function inside it?

I mean something like this (not tested):

diff --git a/block/rbd.c b/block/rbd.c
index f098a89c7b..eb6a839362 100644
--- a/block/rbd.c
+++ b/block/rbd.c
@@ -119,15 +119,8 @@ static char *qemu_rbd_next_tok(char *src, char delim, char **p)
  
      *p = NULL;
  
-    for (end = src; *end; ++end) {
-        if (*end == delim) {
-            break;
-        }
-        if (*end == '\\' && end[1] != '\0') {
-            end++;
-        }
-    }
-    if (*end == delim) {
+    end = qemu_rbd_strchr(src, delim);
+    if (end && *end == delim) {
          *p = end + 1;
          *end = '\0';
      }


The rest LGTM!

Thanks for fixing this issue,
Stefano


