[PATCH 0/1] Fix fstat on FIFOs, part 1

[PATCH 0/1] Fix fstat on FIFOs, part 1

[Ken Brown]

Commit 76dca77f04 had a careless blunder, so this patch reverts it.

Nevertheless, fstat(2) can be made more efficient on FIFOs, and I'm
working on a separate patchset to do this right.  It's worth doing,
because every call to open(2) on a FIFO leads to a call chain

  device_access_denied --> fhaccess --> fstat,

and this is one of the cases where greater efficiency is possible.

Ken Brown (1):
  Revert "Cygwin: fstat_helper: always use handle in call to
    get_file_attribute"

 winsup/cygwin/fhandler_disk_file.cc | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

-- 
2.30.0

[PATCH 1/1] Revert "Cygwin: fstat_helper: always use handle in call to get_file_attribute"

[Ken Brown]

This reverts commit 76dca77f049271e2529c25de8a396e65dbce615d.  That
commit was based on the incorrect assumption that get_stat_handle,
when called on a FIFO in fstat_helper, would always return a handle
that is safe to use for getting the file information.

That assumption is true in many cases but not all.  For example, if
the call to fstat_helper arises from a call to fstat(2) on a FIFO that
has been opened for writing, then get_stat_handle will return a pipe
handle instead of a file handle.
---
 winsup/cygwin/fhandler_disk_file.cc | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/winsup/cygwin/fhandler_disk_file.cc b/winsup/cygwin/fhandler_disk_file.cc
index 5e58688b7..ef9171bbf 100644
--- a/winsup/cygwin/fhandler_disk_file.cc
+++ b/winsup/cygwin/fhandler_disk_file.cc
@@ -394,13 +394,12 @@ fhandler_base::fstat_fs (struct stat *buf)
   return res;
 }
 
-/* Called by fstat_by_handle and fstat_by_name. */
 int __reg2
 fhandler_base::fstat_helper (struct stat *buf)
 {
   IO_STATUS_BLOCK st;
   FILE_COMPRESSION_INFORMATION fci;
-  HANDLE h = get_stat_handle ();      /* Should always be pc.handle(). */
+  HANDLE h = get_stat_handle ();
   PFILE_ALL_INFORMATION pfai = pc.fai ();
   ULONG attributes = pc.file_attributes ();
 
@@ -476,8 +475,8 @@ fhandler_base::fstat_helper (struct stat *buf)
   else if (pc.issocket ())
     buf->st_mode = S_IFSOCK;
 
-  if (!get_file_attribute (h, pc, &buf->st_mode, &buf->st_uid,
-			   &buf->st_gid))
+  if (!get_file_attribute (is_fs_special () && !pc.issocket () ? NULL : h, pc,
+			   &buf->st_mode, &buf->st_uid, &buf->st_gid))
     {
       /* If read-only attribute is set, modify ntsec return value */
       if (::has_attribute (attributes, FILE_ATTRIBUTE_READONLY)
-- 
2.30.0

Re: [PATCH 0/1] Fix fstat on FIFOs, part 1

[Corinna Vinschen]

On Feb  9 10:11, Ken Brown via Cygwin-patches wrote:
> Commit 76dca77f04 had a careless blunder, so this patch reverts it.
> 
> Nevertheless, fstat(2) can be made more efficient on FIFOs, and I'm
> working on a separate patchset to do this right.  It's worth doing,
> because every call to open(2) on a FIFO leads to a call chain
> 
>   device_access_denied --> fhaccess --> fstat,
> 
> and this is one of the cases where greater efficiency is possible.
> 
> Ken Brown (1):
>   Revert "Cygwin: fstat_helper: always use handle in call to
>     get_file_attribute"
> 
>  winsup/cygwin/fhandler_disk_file.cc | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)

Sure, go ahead.


Thanks,
Corinna