[lldb] [Commands] Remove 'append' from 'platform file open' mode

[mgorny]

Summary

Remove File::eOpenOptionAppend from the mode used by 'platform file
open' command. According to POSIX, O_APPEND causes all successive
writes to be done at the end of the file. This effectively makes
the offset argument to 'platform file write' meaningless.

Furthermore, apparently O_APPEND is not implemented reliably everywhere.
The Linux manpage for pwrite(2) suggests that Linux does not respect
O_APPEND there, so the actual behavior would be dependent on how
the vFile:pwrite packet is implemented on the server.

Ideally, the mode used for opening flags would be provided via options.
However, changing the default mode seems to be a reasonable intermediate
solution.

[mgorny]

@jasonmolenda, ping.

[labath]

Sounds reasonable.

The Linux manpage for pwrite(2) suggests that Linux does not respect O_APPEND there,

I guess it would be more correct to say that it "respects" O_APPEND, when it fact POSIX says it shouldn't.

[mgorny]

Thanks, I'll improve the commit message as suggested.

lldb/source/Commands/CommandObjectPlatform.cpp

if (platform_sp) {
           (const OptionPermissions *)m_options.GetGroupWithOption('r');
       if (options_permissions)
         perms = options_permissions->m_permissions;
       else
         perms = lldb::eFilePermissionsUserRW | lldb::eFilePermissionsGroupRW |
                 lldb::eFilePermissionsWorldRead;
       lldb::user_id_t fd = platform_sp->OpenFile(
           FileSpec(cmd_line),
-          File::eOpenOptionReadWrite | File::eOpenOptionAppend |
-               File::eOpenOptionCanCreate,
+          File::eOpenOptionReadWrite | File::eOpenOptionCanCreate,
           perms, error);
       if (error.Success()) {
         result.AppendMessageWithFormat("File Descriptor = %" PRIu64 "\n", fd);
         result.SetStatus(eReturnStatusSuccessFinishResult);
       } else {
         result.AppendError(error.AsCString());
       }
     } else {

lldb/test/API/functionalities/gdb_remote_client/TestGDBRemotePlatformFile.py

def test_file(self):
                        [r"File Descriptor = 16"])
             self.match("platform file read 16 -o 11 -c 13",
                        [r"Return = 11\nData = \"frobnicator\""])
             self.match("platform file write 16 -o 11 -d teststring",
                        [r"Return = 10"])
             self.match("platform file close 16",
                        [r"file 16 closed."])
             self.assertPacketLogContains([
-                "vFile:open:2f736f6d652f66696c652e747874,0000020a,000001ed",
+                "vFile:open:2f736f6d652f66696c652e747874,00000202,000001ed",
                 "vFile:pread:10,d,b",
                 "vFile:pwrite:10,b,teststring",
                 "vFile:close:10",
                 ])
         finally:
             self.dbg.GetSelectedPlatform().DisconnectRemote()
 
     def test_file_fail(self):
def test_file_fail(self):
                        error=True)
             self.match("platform file write 16 -o 11 -d teststring",
                        [r"error: Invalid argument"],
                        error=True)
             self.match("platform file close 16",
                        [r"error: Invalid argument"],
                        error=True)
             self.assertPacketLogContains([
-                "vFile:open:2f736f6d652f66696c652e747874,0000020a,000001ed",
+                "vFile:open:2f736f6d652f66696c652e747874,00000202,000001ed",
                 "vFile:pread:10,d,b",
                 "vFile:pwrite:10,b,teststring",
                 "vFile:close:10",
                 ])
         finally:
             self.dbg.GetSelectedPlatform().DisconnectRemote()