From 603ef545bdbdbf7495e1a0bbabffb8741fc2a5bb Mon Sep 17 00:00:00 2001 From: Corinna Vinschen Date: Thu, 25 Aug 2011 13:35:43 +0000 Subject: * fhandler.cc (fhandler_base::open): Never open files with 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. --- winsup/cygwin/ChangeLog | 7 +++++++ winsup/cygwin/fhandler.cc | 42 ++++++++++++++++++++++++++++++------------ 2 files changed, 37 insertions(+), 12 deletions(-) diff --git a/winsup/cygwin/ChangeLog b/winsup/cygwin/ChangeLog index 1308ffa39..db2d9201a 100644 --- a/winsup/cygwin/ChangeLog +++ b/winsup/cygwin/ChangeLog @@ -1,3 +1,10 @@ +2011-08-25 Corinna Vinschen + + * fhandler.cc (fhandler_base::open): Never open files with + 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. + 2011-08-24 Corinna Vinschen * thread.cc (pthread::pthread): Drop setting parent_tls. Call diff --git a/winsup/cygwin/fhandler.cc b/winsup/cygwin/fhandler.cc index 4e1c0a6c1..722f11102 100644 --- a/winsup/cygwin/fhandler.cc +++ b/winsup/cygwin/fhandler.cc @@ -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 ()); -- cgit v1.2.3