diff options
Diffstat (limited to 'winsup/cygwin/fhandler_disk_file.cc')
| -rw-r--r-- | winsup/cygwin/fhandler_disk_file.cc | 121 |
1 files changed, 110 insertions, 11 deletions
diff --git a/winsup/cygwin/fhandler_disk_file.cc b/winsup/cygwin/fhandler_disk_file.cc index a57427b4f..9cebbe475 100644 --- a/winsup/cygwin/fhandler_disk_file.cc +++ b/winsup/cygwin/fhandler_disk_file.cc @@ -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); } @@ -1373,6 +1373,35 @@ fhandler_disk_file::open (int flags, mode_t 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) { /* Unfortunately NT allows to open directories for writing, but that's @@ -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); |