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* fhandler.cc (fhandler_base::open): Drop local create_options variable.

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Use options member instead.
	* fhandler.h (class fhandler_base): Change type of access member to
	ACCESS_MASK.  Change get_access and set_access methods accordingly.
	Add options member.  Add get_options and set_options methods.
	(class fhandler_disk_file): Add prw_handle.
	(fhandler_disk_file::prw_open): Declare.
	(fhandler_disk_file::close): Declare.
	(fhandler_disk_file::dup): Declare.
	(fhandler_disk_file::fixup_after_fork): Declare.
	* fhandler_disk_file.cc (fhandler_disk_file::fhandler_disk_file):
	Initialize prw_handle to NULL.
	(fhandler_disk_file::close): Close prw_handle.
	(fhandler_disk_file::dup): New method.
	(fhandler_disk_file::fixup_after_fork): Set prw_handle to NULL since
	prw_handle is not inherited.
	(fhandler_disk_file::prw_open): New method.  Add long comment to
	explain current behaviour.
	(fhandler_disk_file::pread): Revert previous change.  Change to use
	prw_handle if possible.
	(fhandler_disk_file::pwrite): Change to use prw_handle if possible.
This commit is contained in:
Corinna Vinschen
2011-06-17 11:04:44 +00:00
parent a716252619
commit c36cd56c54
4 changed files with 155 additions and 21 deletions
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121
winsup/cygwin/fhandler_disk_file.cc
View File

@ -1356,12 +1356,12 @@ fhandler_base::utimens_fs (const struct timespec *tvp)
}
fhandler_disk_file::fhandler_disk_file () :
fhandler_base ()
fhandler_base (), prw_handle (NULL)
{
}
fhandler_disk_file::fhandler_disk_file (path_conv &pc) :
fhandler_base ()
fhandler_base (), prw_handle (NULL)
{
set_name (pc);
}
@ -1372,6 +1372,35 @@ fhandler_disk_file::open (int flags, mode_t mode)
return open_fs (flags, mode);
}
int
fhandler_disk_file::close ()
{
if (prw_handle)
NtClose (prw_handle);
return fhandler_base::close ();
}
int
fhandler_disk_file::dup (fhandler_base *child)
{
fhandler_disk_file *fhc = (fhandler_disk_file *) child;
int ret = fhandler_base::dup (child);
if (!ret && prw_handle
&& !DuplicateHandle (GetCurrentProcess (), prw_handle,
GetCurrentProcess (), &fhc->prw_handle,
0, TRUE, DUPLICATE_SAME_ACCESS))
prw_handle = NULL;
return ret;
}
void
fhandler_disk_file::fixup_after_fork (HANDLE parent)
{
prw_handle = NULL;
fhandler_base::fixup_after_fork (parent);
}
int
fhandler_base::open_fs (int flags, mode_t mode)
{
@ -1412,6 +1441,73 @@ out:
return res;
}
/* POSIX demands that pread/pwrite don't change the current file position.
While NtReadFile/NtWriteFile support atomic seek-and-io, both change the
file pointer if the file handle has been opened for synchonous I/O.
Using this handle for pread/pwrite would break atomicity, because the
read/write operation would have to be followed by a seek back to the old
file position. What we do is to open another handle to the file on the
first call to either pread or pwrite. This is used for any subsequent
pread/pwrite. Thus the current file position of the "normal" file
handle is not touched.
FIXME:
Note that this is just a hack. The problem with this approach is that
a change to the file permissions might disallow to open the file with
the required permissions to read or write. This appears to be a border case,
but that's exactly what git does. It creates the file for reading and
writing and after writing it, it chmods the file to read-only. Then it
calls pread on the file to examine the content. This works, but if git
would use the original handle to pwrite to the file, it would be broken
with our approach.
One way to implement this is to open the pread/pwrite handle right at
file open time. We would simply maintain two handles, which wouldn't
be much of a problem given how we do that for other fhandler types as
well.
However, ultimately fhandler_disk_file should become a derived class of
fhandler_base_overlapped. Each raw_read or raw_write would fetch the
actual file position, read/write from there, and then set the file
position again. Fortunately, while the file position is not maintained
by the I/O manager, it can be fetched and set to a new value by all
processes holding a handle to that file object. Pread and pwrite differ
from raw_read and raw_write just by not touching the current file pos.
Actually they could be merged with raw_read/raw_write if we add a position
parameter to the latter. */
int
fhandler_disk_file::prw_open (bool write)
{
NTSTATUS status;
IO_STATUS_BLOCK io;
OBJECT_ATTRIBUTES attr;
/* First try to open with the original access mask */
ACCESS_MASK access = get_access ();
pc.init_reopen_attr (&attr, get_handle ());
status = NtOpenFile (&prw_handle, access, &attr, &io,
FILE_SHARE_VALID_FLAGS, get_options ());
if (status == STATUS_ACCESS_DENIED)
{
/* If we get an access denied, chmod has been called. Try again
with just the required rights to perform the called function. */
access &= write ? ~GENERIC_READ : ~GENERIC_WRITE;
status = NtOpenFile (&prw_handle, access, &attr, &io,
FILE_SHARE_VALID_FLAGS, get_options ());
}
debug_printf ("%x = NtOpenFile (%p, %x, %S, io, %x, %x)",
status, prw_handle, access, pc.get_nt_native_path (),
FILE_SHARE_VALID_FLAGS, get_options ());
if (!NT_SUCCESS (status))
{
__seterrno_from_nt_status (status);
return -1;
}
return 0;
}
ssize_t __stdcall
fhandler_disk_file::pread (void *buf, size_t count, _off64_t offset)
{
@ -1429,7 +1525,9 @@ fhandler_disk_file::pread (void *buf, size_t count, _off64_t offset)
IO_STATUS_BLOCK io;
LARGE_INTEGER off = { QuadPart:offset };
status = NtReadFile (get_handle (), NULL, NULL, NULL, &io, buf, count,
if (!prw_handle && prw_open (false))
goto non_atomic;
status = NtReadFile (prw_handle, NULL, NULL, NULL, &io, buf, count,
&off, NULL);
if (!NT_SUCCESS (status))
{
@ -1440,15 +1538,15 @@ fhandler_disk_file::pread (void *buf, size_t count, _off64_t offset)
}
if (status == (NTSTATUS) STATUS_ACCESS_VIOLATION)
{
if (is_at_eof (get_handle ()))
if (is_at_eof (prw_handle))
return 0;
switch (mmap_is_attached_or_noreserve (buf, count))
{
case MMAP_NORESERVE_COMMITED:
status = NtReadFile (get_handle (), NULL, NULL, NULL, &io,
status = NtReadFile (prw_handle, NULL, NULL, NULL, &io,
buf, count, &off, NULL);
if (NT_SUCCESS (status))
goto success;
return io.Information;
break;
case MMAP_RAISE_SIGBUS:
raise (SIGBUS);
@ -1459,12 +1557,9 @@ fhandler_disk_file::pread (void *buf, size_t count, _off64_t offset)
__seterrno_from_nt_status (status);
return -1;
}
success:
lseek (-io.Information, SEEK_CUR);
return io.Information;
}
non_atomic:
/* Text mode stays slow and non-atomic. */
ssize_t res;
_off64_t curpos = lseek (0, SEEK_CUR);
@ -1499,7 +1594,9 @@ fhandler_disk_file::pwrite (void *buf, size_t count, _off64_t offset)
IO_STATUS_BLOCK io;
LARGE_INTEGER off = { QuadPart:offset };
status = NtWriteFile (get_handle (), NULL, NULL, NULL, &io, buf, count,
if (!prw_handle && prw_open (true))
goto non_atomic;
status = NtWriteFile (prw_handle, NULL, NULL, NULL, &io, buf, count,
&off, NULL);
if (!NT_SUCCESS (status))
{
@ -1508,6 +1605,8 @@ fhandler_disk_file::pwrite (void *buf, size_t count, _off64_t offset)
}
return io.Information;
}
non_atomic:
/* Text mode stays slow and non-atomic. */
int res;
_off64_t curpos = lseek (0, SEEK_CUR);