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Cygwin: FIFO: add shared memory 

Even though we currently allow a FIFO to be opened for reading only
once, we can still have more than one reader open because of dup and
fork.  Add a named shared memory section accessible to all readers of
a given FIFO.  In future commits we will add information needed by all
readers to this section

Add a class fifo_shmem_t that lets us access this information.

Add a method create_shmem that is called when a reader opens, and add
a method reopen_shmem that is called by dup, fork, and exec.  (Each
new reader needs its own view of the shared memory.)
This commit is contained in:
Ken Brown 2020-03-17 12:29:56 -04:00
parent 71726ba70b
commit 878eb22462
2 changed files with 106 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

13
winsup/cygwin/fhandler.h
View File

@ -1300,6 +1300,11 @@ struct fifo_client_handler
int pipe_state ();
};
/* Info needed by all readers of a FIFO, stored in named shared memory. */
class fifo_shmem_t
{
};
class fhandler_fifo: public fhandler_base
{
/* Handles to named events shared by all fhandlers for a given FIFO. */
@ -1319,6 +1324,10 @@ class fhandler_fifo: public fhandler_base
af_unix_spinlock_t _fifo_client_lock;
bool reader, writer, duplexer;
size_t max_atomic_write;
HANDLE shmem_handle;
fifo_shmem_t *shmem;
bool __reg2 wait (HANDLE);
static NTSTATUS npfs_handle (HANDLE &);
HANDLE create_pipe_instance (bool);
@ -1330,6 +1339,9 @@ class fhandler_fifo: public fhandler_base
void record_connection (fifo_client_handler&,
fifo_client_connect_state = fc_connected);
int create_shmem ();
int reopen_shmem ();
public:
fhandler_fifo ();
bool hit_eof ();
@ -1341,6 +1353,7 @@ public:
DWORD fifo_reader_thread_func ();
void fifo_client_lock () { _fifo_client_lock.lock (); }
void fifo_client_unlock () { _fifo_client_lock.unlock (); }
int open (int, mode_t);
off_t lseek (off_t offset, int whence);
int close ();

97
winsup/cygwin/fhandler_fifo.cc
View File

@ -70,7 +70,8 @@ fhandler_fifo::fhandler_fifo ():
read_ready (NULL), write_ready (NULL), writer_opening (NULL),
cancel_evt (NULL), thr_sync_evt (NULL), _maybe_eof (false), nhandlers (0),
reader (false), writer (false), duplexer (false),
max_atomic_write (DEFAULT_PIPEBUFSIZE)
max_atomic_write (DEFAULT_PIPEBUFSIZE),
shmem_handle (NULL), shmem (NULL)
{
pipe_name_buf[0] = L'\0';
need_fork_fixup (true);
@ -441,6 +442,67 @@ canceled:
return 0;
}
int
fhandler_fifo::create_shmem ()
{
HANDLE sect;
OBJECT_ATTRIBUTES attr;
NTSTATUS status;
LARGE_INTEGER size = { .QuadPart = sizeof (fifo_shmem_t) };
SIZE_T viewsize = sizeof (fifo_shmem_t);
PVOID addr = NULL;
UNICODE_STRING uname;
WCHAR shmem_name[MAX_PATH];
__small_swprintf (shmem_name, L"fifo-shmem.%08x.%016X", get_dev (),
get_ino ());
RtlInitUnicodeString (&uname, shmem_name);
InitializeObjectAttributes (&attr, &uname, OBJ_INHERIT,
get_shared_parent_dir (), NULL);
status = NtCreateSection (&sect, STANDARD_RIGHTS_REQUIRED | SECTION_QUERY
| SECTION_MAP_READ | SECTION_MAP_WRITE,
&attr, &size, PAGE_READWRITE, SEC_COMMIT, NULL);
if (status == STATUS_OBJECT_NAME_COLLISION)
status = NtOpenSection (&sect, STANDARD_RIGHTS_REQUIRED | SECTION_QUERY
| SECTION_MAP_READ | SECTION_MAP_WRITE, &attr);
if (!NT_SUCCESS (status))
{
__seterrno_from_nt_status (status);
return -1;
}
status = NtMapViewOfSection (sect, NtCurrentProcess (), &addr, 0, viewsize,
NULL, &viewsize, ViewShare, 0, PAGE_READWRITE);
if (!NT_SUCCESS (status))
{
NtClose (sect);
__seterrno_from_nt_status (status);
return -1;
}
shmem_handle = sect;
shmem = (fifo_shmem_t *) addr;
return 0;
}
/* shmem_handle must be valid when this is called. */
int
fhandler_fifo::reopen_shmem ()
{
NTSTATUS status;
SIZE_T viewsize = sizeof (fifo_shmem_t);
PVOID addr = NULL;
status = NtMapViewOfSection (shmem_handle, NtCurrentProcess (), &addr,
0, viewsize, NULL, &viewsize, ViewShare,
0, PAGE_READWRITE);
if (!NT_SUCCESS (status))
{
__seterrno_from_nt_status (status);
return -1;
}
shmem = (fifo_shmem_t *) addr;
return 0;
}
int
fhandler_fifo::open (int flags, mode_t)
{
@ -501,12 +563,15 @@ fhandler_fifo::open (int flags, mode_t)
goto err_close_write_ready;
}
/* If we're reading, signal read_ready and start the fifo_reader_thread. */
/* If we're reading, signal read_ready, create the shared memory,
and start the fifo_reader_thread. */
if (reader)
{
SetEvent (read_ready);
if (!(cancel_evt = create_event ()))
if (create_shmem () < 0)
goto err_close_writer_opening;
if (!(cancel_evt = create_event ()))
goto err_close_shmem;
if (!(thr_sync_evt = create_event ()))
goto err_close_cancel_evt;
new cygthread (fifo_reader_thread, this, "fifo_reader", thr_sync_evt);
@ -615,6 +680,9 @@ err_close_reader:
return 0;
err_close_cancel_evt:
NtClose (cancel_evt);
err_close_shmem:
NtUnmapViewOfSection (NtCurrentProcess (), shmem);
NtClose (shmem_handle);
err_close_writer_opening:
NtClose (writer_opening);
err_close_write_ready:
@ -944,6 +1012,10 @@ fhandler_fifo::close ()
dup/fork/exec; we should only reset read_ready when the last
one closes. */
ResetEvent (read_ready);
if (shmem)
NtUnmapViewOfSection (NtCurrentProcess (), shmem);
if (shmem_handle)
NtClose (shmem_handle);
}
if (read_ready)
NtClose (read_ready);
@ -1014,6 +1086,15 @@ fhandler_fifo::dup (fhandler_base *child, int flags)
/* Make sure the child starts unlocked. */
fhf->fifo_client_unlock ();
if (!DuplicateHandle (GetCurrentProcess (), shmem_handle,
GetCurrentProcess (), &fhf->shmem_handle,
0, !(flags & O_CLOEXEC), DUPLICATE_SAME_ACCESS))
{
__seterrno ();
goto err_close_writer_opening;
}
if (fhf->reopen_shmem () < 0)
goto err_close_shmem_handle;
fifo_client_lock ();
for (i = 0; i < nhandlers; i++)
{
@ -1044,7 +1125,10 @@ err_close_cancel_evt:
err_close_handlers:
for (int j = 0; j < i; j++)
fhf->fc_handler[j].close ();
/* err_close_writer_opening: */
NtUnmapViewOfSection (GetCurrentProcess (), fhf->shmem);
err_close_shmem_handle:
NtClose (fhf->shmem_handle);
err_close_writer_opening:
NtClose (fhf->writer_opening);
err_close_write_ready:
NtClose (fhf->write_ready);
@ -1066,6 +1150,9 @@ fhandler_fifo::fixup_after_fork (HANDLE parent)
/* Make sure the child starts unlocked. */
fifo_client_unlock ();
fork_fixup (parent, shmem_handle, "shmem_handle");
if (reopen_shmem () < 0)
api_fatal ("Can't reopen shared memory during fork, %E");
fifo_client_lock ();
for (int i = 0; i < nhandlers; i++)
fork_fixup (parent, fc_handler[i].h, "fc_handler[].h");
@ -1087,6 +1174,8 @@ fhandler_fifo::fixup_after_exec ()
/* Make sure the child starts unlocked. */
fifo_client_unlock ();
if (reopen_shmem () < 0)
api_fatal ("Can't reopen shared memory during exec, %E");
if (!(cancel_evt = create_event ()))
api_fatal ("Can't create reader thread cancel event during exec, %E");
if (!(thr_sync_evt = create_event ()))