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* fhandler.cc (fhandler_base::open): Never open files with

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FILE_OVERWITE/FILE_OVERWRITE_IF.  Set file size to 0 explicitely if
	regular, existing file has been opened for writing with O_TRUNC flag
	set.  Explain why.
This commit is contained in:
Corinna Vinschen
2011-08-25 13:35:43 +00:00
parent 929a140824
commit 603ef545bd
2 changed files with 37 additions and 12 deletions
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42
winsup/cygwin/fhandler.cc
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@@ -540,20 +540,12 @@ fhandler_base::open (int flags, mode_t mode)
break;
}
if ((flags & O_TRUNC) && ((flags & O_ACCMODE) != O_RDONLY))
{
if (flags & O_CREAT)
create_disposition = FILE_OVERWRITE_IF;
else
create_disposition = FILE_OVERWRITE;
}
else if (flags & O_CREAT)
create_disposition = FILE_OPEN_IF;
else
create_disposition = FILE_OPEN;
/* Don't use the FILE_OVERWRITE{_IF} flags here. See below for an
explanation, why that's not such a good idea. */
if ((flags & O_EXCL) && (flags & O_CREAT))
create_disposition = FILE_CREATE;
else
create_disposition = (flags & O_CREAT) ? FILE_OPEN_IF : FILE_OPEN;
if (get_device () == FH_FS)
{
@@ -664,6 +656,32 @@ fhandler_base::open (int flags, mode_t mode)
if (io.Information == FILE_CREATED && has_acls ())
set_file_attribute (fh, pc, ILLEGAL_UID, ILLEGAL_GID, S_JUSTCREATED | mode);
/* If you O_TRUNC a file on Linux, the data is truncated, but the EAs are
preserved. If you open a file on Windows with FILE_OVERWRITE{_IF} or
FILE_SUPERSEDE, all streams are truncated, including the EAs. So we don't
use the FILE_OVERWRITE{_IF} flags, but instead just open the file and set
the size of the data stream explicitely to 0. Apart from being more Linux
compatible, this implementation has the pleasant side-effect to be more
than 5% faster than using FILE_OVERWRITE{_IF} (tested on W7 32 bit). */
if ((flags & O_TRUNC)
&& (flags & O_ACCMODE) != O_RDONLY
&& io.Information != FILE_CREATED
&& get_device () == FH_FS)
{
FILE_END_OF_FILE_INFORMATION feofi = { EndOfFile:{ QuadPart:0 } };
status = NtSetInformationFile (fh, &io, &feofi, sizeof feofi,
FileEndOfFileInformation);
/* In theory, truncating the file should never fail, since the opened
handle has FILE_READ_DATA permissions, which is all you need to
be allowed to truncate a file. Better safe than sorry. */
if (!NT_SUCCESS (status))
{
__seterrno_from_nt_status (status);
NtClose (fh);
goto done;
}
}
set_io_handle (fh);
set_flags (flags, pc.binmode ());