[PATCH v6 08/11] 9p: add P9_ERRMAX for 9p2000 and 9p2000.u

[Christian Schoenebeck <linux_oss@crudebyte.com>]

Add P9_ERRMAX macro to 9P protocol header which reflects the maximum
error string length of Rerror replies for 9p2000 and 9p2000.u protocol
versions. Unfortunately a maximum error string length is not defined by
the 9p2000 spec, picking 128 as value for now, as this seems to be a
common max. size for POSIX error strings in practice.

9p2000.L protocol version uses Rlerror replies instead which does not
contain an error string.

Signed-off-by: Christian Schoenebeck <linux_oss@crudebyte.com>
---

This could probably be merged with the next patch, on doubt I posted it
separately as squashing is easy. The advantage of a separate patch is
making the discussion of the chosen value of max. 128 bytes more
prominent.

 include/net/9p/9p.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/net/9p/9p.h b/include/net/9p/9p.h
index 24a509f559ee..13abe013af21 100644
--- a/include/net/9p/9p.h
+++ b/include/net/9p/9p.h
@@ -331,6 +331,9 @@ enum p9_qid_t {
 /* size of header for zero copy read/write */
 #define P9_ZC_HDR_SZ 4096
 
+/* maximum length of an error string */
+#define P9_ERRMAX 128
+
 /**
  * struct p9_qid - file system entity information
  * @type: 8-bit type &p9_qid_t
-- 
2.30.2