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From: Philippe Cerfon <>
Date: Tue, 30 May 2023 13:25:38 +0200	[thread overview]
Message-ID: <> (raw)

[-- Attachment #1: Type: text/plain, Size: 1361 bytes --]

Hey there.

Linux exports XATTR_{NAME,SIZE,LIST}_MAX in it's linux/limits.h and
e.g. the CPython interpreter uses them for it's XATTRs functions.

I made a corresponding PR at CPython to get the code built
for Cygwin, but right now this would fail due to the missing
XATTR_*_MAX symbols.

The attached patch below would add them to cygwin/limits.h.

But beware, I'm absolutely no Windows/Cygwin expert ^^ - so whether
the values I've chosen are actually correct, is more guesswork rather
than definite knowledge.

As written in the commit message, I think:

though I have no idea, whether these are just lower boundaries used by
Cygwin, while e.g. Windows itself might set longer names or value
lenghts, and thus - when Cygwin would try to read such - it might get
into troubles (or rather e.g. CPython, as it's buffers wouldn't
suffice to read the EA respectively XATTR.

Neither to i have an idea about XATTR_LIST_MAX. I'm not even 100% sure
what it means (I guess the max number of XATTRs per file). Not to
speak about whether there's such maximum for Windows EAs,
And again - as above - what would happen if Windows itself would set
more than that limit and within Cygwin one would try to read/list all.


[-- Attachment #2: 0001-export-XATTR_-NAME-SIZE-LIST-_MAX.patch --]
[-- Type: text/x-patch, Size: 1250 bytes --]

From 824bcdf053bfb86570c7edda3c018626dc857a8b Mon Sep 17 00:00:00 2001
From: Philippe Cerfon <>
Date: Tue, 30 May 2023 13:16:18 +0200

These are used for example by CPython. XATTR_NAME_MAX should correspond to

It's unclear whether Windows imposes a maximum number of EA's per file and which
value should be used for XATTR_LIST_MAX, so for now Linux' value.

Signed-off-by: Philippe Cerfon <>
 winsup/cygwin/include/cygwin/limits.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/winsup/cygwin/include/cygwin/limits.h b/winsup/cygwin/include/cygwin/limits.h
index aefc7c7bd..939ab4f38 100644
--- a/winsup/cygwin/include/cygwin/limits.h
+++ b/winsup/cygwin/include/cygwin/limits.h
@@ -56,4 +56,11 @@ details. */
 #define __PATH_MAX 4096
 #define __PIPE_BUF 4096
+/* Keep in sync with MAX_EA_NAME_LEN respectively MAX_EA_VALUE_LEN in
+ * winsup/cygwin/ but don not use values that exceed their Linux
+ * counterparts as defined in linux/limits.h. */
+#define XATTR_NAME_MAX 255
+#define XATTR_SIZE_MAX 65536
+#define XATTR_LIST_MAX 65536
 #endif /* _CYGWIN_LIMITS_H__ */

             reply	other threads:[~2023-05-30 11:25 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-05-30 11:25 Philippe Cerfon [this message]
2023-05-30 11:35 ` Philippe Cerfon
2023-05-30 20:04 ` [PATCH] include/cygwin/limits.h: add XATTR_{NAME,SIZE,LIST}_MAX Brian Inglis
2023-05-30 21:59   ` Philippe Cerfon

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