[PATCH v2 1/8] syscalls.cc: unlink_nt: Try FILE_DISPOSITION_IGNORE_READONLY_ATTRIBUTE

[Corinna Vinschen]

Hi Ben,

On Jan 20 17:10, Ben Wijen wrote:
> Implement wincap.has_posix_unlink_semantics_with_ignore_readonly and when set
> skip setting/clearing of READONLY attribute and instead use
> FILE_DISPOSITION_IGNORE_READONLY_ATTRIBUTE
> ---
>  winsup/cygwin/ntdll.h     |  3 ++-
>  winsup/cygwin/syscalls.cc | 14 +++++-----
>  winsup/cygwin/wincap.cc   | 11 ++++++++
>  winsup/cygwin/wincap.h    | 56 ++++++++++++++++++++-------------------
>  4 files changed, 49 insertions(+), 35 deletions(-)
> 
> diff --git a/winsup/cygwin/ntdll.h b/winsup/cygwin/ntdll.h
> index d4f6aaf45..7eee383dd 100644
> --- a/winsup/cygwin/ntdll.h
> +++ b/winsup/cygwin/ntdll.h
> @@ -497,7 +497,8 @@ enum {
>    FILE_DISPOSITION_DELETE				= 0x01,
>    FILE_DISPOSITION_POSIX_SEMANTICS			= 0x02,
>    FILE_DISPOSITION_FORCE_IMAGE_SECTION_CHECK		= 0x04,
> -  FILE_DISPOSITION_ON_CLOSE				= 0x08
> +  FILE_DISPOSITION_ON_CLOSE				= 0x08,
> +  FILE_DISPOSITION_IGNORE_READONLY_ATTRIBUTE		= 0x10,
>  };
>  
>  enum
> diff --git a/winsup/cygwin/syscalls.cc b/winsup/cygwin/syscalls.cc
> index 4742c6653..2e50ad7d5 100644
> --- a/winsup/cygwin/syscalls.cc
> +++ b/winsup/cygwin/syscalls.cc
> @@ -709,14 +709,11 @@ _unlink_nt (path_conv &pc, bool shareable)
>  			   flags);

A few lines above, FILE_WRITE_ATTRIBUTES is added to the
access mask, if the file is R/O.  This, too, depends on
wincap.has_posix_unlink_semantics_with_ignore_readonly().

>        if (!NT_SUCCESS (status))
>  	goto out;
> -      /* Why didn't the devs add a FILE_DELETE_IGNORE_READONLY_ATTRIBUTE
> -	 flag just like they did with FILE_LINK_IGNORE_READONLY_ATTRIBUTE
> -	 and FILE_LINK_IGNORE_READONLY_ATTRIBUTE???
> -
> -         POSIX unlink semantics are nice, but they still fail if the file
> +      /* POSIX unlink semantics are nice, but they still fail if the file
>  	 has the R/O attribute set.  Removing the file is very much a safe
>  	 bet afterwards, so, no transaction. */

This comment should contain a short comment "W10 1809+, blah blah",
analogue to the comment in line 698 in terms of 1709+ ("++"?  Oops,
fix typo...).


> -      if (pc.file_attributes () & FILE_ATTRIBUTE_READONLY)
> +      if (!wincap.has_posix_unlink_semantics_with_ignore_readonly ()
> +          && (pc.file_attributes () & FILE_ATTRIBUTE_READONLY))

I'd invert the test order here.  On 1809+ systems, the majority of
systems these days, the first test is always true, but it's always
checked, even if the file is not R/O.  First checking for R/O would
reduce the hits on the "with_ignore_readonly" check.

>  	{
>  	  status = NtSetAttributesFile (fh, pc.file_attributes ()
>  					    & ~FILE_ATTRIBUTE_READONLY);
> @@ -727,10 +724,13 @@ _unlink_nt (path_conv &pc, bool shareable)
>  	    }
>  	}
>        fdie.Flags = FILE_DISPOSITION_DELETE | FILE_DISPOSITION_POSIX_SEMANTICS;
> +      if(wincap.has_posix_unlink_semantics_with_ignore_readonly ())
          ^^^
          space
> +          fdie.Flags |= FILE_DISPOSITION_IGNORE_READONLY_ATTRIBUTE;
         ^^^^
         indentation 2, not 4.

>        status = NtSetInformationFile (fh, &io, &fdie, sizeof fdie,
>  				     FileDispositionInformationEx);
>        /* Restore R/O attribute in case we have multiple hardlinks. */
> -      if (pc.file_attributes () & FILE_ATTRIBUTE_READONLY)
> +      if (!wincap.has_posix_unlink_semantics_with_ignore_readonly ()
> +          && (pc.file_attributes () & FILE_ATTRIBUTE_READONLY))

Same here.

Actually, on second thought, what about introducing another bool at the
start of the posix handling, along the lines of

   const bool needs_ro_handling =
     (pc.file_attributes () & FILE_ATTRIBUTE_READONLY)
     && !wincap.has_posix_unlink_semantics_with_ignore_readonly ();

and then check for needs_ro_handling throughout?


Thanks,
Corinna