Utilize more frequently supported file access modes
* java/org/gnu/emacs/EmacsSafThread.java (openDocument1): Use plain r or w where possible, as the fileio stuff is now better prepared for FIFOs. (openDocument): New argument READ. * java/org/gnu/emacs/EmacsService.java (openDocument): New argument READ. * src/android.c (android_init_emacs_service): Adjust correspondingly. * src/androidvfs.c (android_saf_file_open): Don't support O_APPEND. Pass read as well as trunc and write.
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Po Lu
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4 changed files with 85 additions and 41 deletions
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@ -1565,8 +1565,9 @@ In addition, arbitrary runtime exceptions (such as
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signal. */
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public ParcelFileDescriptor
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openDocument1 (String uri, String documentId, boolean write,
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boolean truncate, CancellationSignal signal)
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openDocument1 (String uri, String documentId, boolean read,
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boolean write, boolean truncate,
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CancellationSignal signal)
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throws Throwable
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{
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Uri treeUri, documentUri;
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@ -1586,10 +1587,19 @@ In addition, arbitrary runtime exceptions (such as
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if (write)
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{
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if (truncate)
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mode = "rwt";
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if (read)
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{
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if (truncate)
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mode = "rwt";
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else
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mode = "rw";
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}
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else
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mode = "rw";
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/* Set mode to w when WRITE && !READ, disregarding TRUNCATE.
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In contradiction with the ContentResolver documentation,
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document providers seem to truncate files whenever w is
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specified, at least superficially. */
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mode = "w";
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}
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else
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mode = "r";
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@ -1597,14 +1607,15 @@ In addition, arbitrary runtime exceptions (such as
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fileDescriptor
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= resolver.openFileDescriptor (documentUri, mode,
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signal);
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Log.d (TAG, "openDocument1: " + mode + " " + fileDescriptor);
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/* If a writable file descriptor is requested and TRUNCATE is set,
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then probe the file descriptor to detect if it is actually
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readable. If not, close this file descriptor and reopen it
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with MODE set to rw; some document providers granting access to
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Samba shares don't implement rwt, but these document providers
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invariably truncate the file opened even when the mode is
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merely rw.
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/* If a writable on-disk file descriptor is requested and TRUNCATE
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is set, then probe the file descriptor to detect if it is
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actually readable. If not, close this file descriptor and
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reopen it with MODE set to rw; some document providers granting
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access to Samba shares don't implement rwt, but these document
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providers invariably truncate the file opened even when the
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mode is merely w.
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This may be ascribed to a mix-up in Android's documentation
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regardin DocumentsProvider: the `openDocument' function is only
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@ -1612,7 +1623,7 @@ In addition, arbitrary runtime exceptions (such as
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implementation of the `openFile' function (which documents rwt)
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delegates to `openDocument'. */
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if (write && truncate && fileDescriptor != null
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if (read && write && truncate && fileDescriptor != null
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&& !EmacsNative.ftruncate (fileDescriptor.getFd ()))
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{
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try
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@ -1647,15 +1658,13 @@ In addition, arbitrary runtime exceptions (such as
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TRUNCATE and the document already exists, truncate its contents
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before returning.
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On Android 9.0 and earlier, always open the document in
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``read-write'' mode; this instructs the document provider to
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return a seekable file that is stored on disk and returns correct
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file status.
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If READ && WRITE, open the file under either the `rw' or `rwt'
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access mode, which implies that the value must be a seekable
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on-disk file. If WRITE && !READ or TRUNC && WRITE, also truncate
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the file after it is opened.
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Under newer versions of Android, open the document in a
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non-writable mode if WRITE is false. This is possible because
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these versions allow Emacs to explicitly request a seekable
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on-disk file.
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If only READ or WRITE is set, value may be a non-seekable FIFO or
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one end of a socket pair.
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Value is NULL upon failure or a parcel file descriptor upon
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success. Call `ParcelFileDescriptor.close' on this file
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@ -1667,7 +1676,8 @@ In addition, arbitrary runtime exceptions (such as
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public ParcelFileDescriptor
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openDocument (final String uri, final String documentId,
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final boolean write, final boolean truncate)
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final boolean read, final boolean write,
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final boolean truncate)
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{
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Object tem;
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@ -1677,8 +1687,8 @@ In addition, arbitrary runtime exceptions (such as
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runObject (CancellationSignal signal)
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throws Throwable
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{
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return openDocument1 (uri, documentId, write, truncate,
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signal);
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return openDocument1 (uri, documentId, read,
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write, truncate, signal);
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}
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});
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@ -1537,15 +1537,13 @@ In addition, arbitrary runtime exceptions (such as
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TRUNCATE and the document already exists, truncate its contents
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before returning.
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On Android 9.0 and earlier, always open the document in
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``read-write'' mode; this instructs the document provider to
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return a seekable file that is stored on disk and returns correct
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file status.
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If READ && WRITE, open the file under either the `rw' or `rwt'
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access mode, which implies that the value must be a seekable
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on-disk file. If TRUNC && WRITE, also truncate the file after it
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is opened.
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Under newer versions of Android, open the document in a
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non-writable mode if WRITE is false. This is possible because
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these versions allow Emacs to explicitly request a seekable
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on-disk file.
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If only READ or WRITE is set, value may be a non-seekable FIFO or
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one end of a socket pair.
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Value is NULL upon failure or a parcel file descriptor upon
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success. Call `ParcelFileDescriptor.close' on this file
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@ -1555,8 +1553,8 @@ In addition, arbitrary runtime exceptions (such as
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UnsupportedOperationException may be thrown upon failure. */
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public ParcelFileDescriptor
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openDocument (String uri, String documentId, boolean write,
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boolean truncate)
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openDocument (String uri, String documentId,
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boolean read, boolean write, boolean truncate)
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{
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/* Start the thread used to run SAF requests if it isn't already
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running. */
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@ -1567,7 +1565,7 @@ In addition, arbitrary runtime exceptions (such as
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storageThread.start ();
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}
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return storageThread.openDocument (uri, documentId, write,
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return storageThread.openDocument (uri, documentId, read, write,
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truncate);
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}
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@ -1574,7 +1574,7 @@ android_init_emacs_service (void)
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"(Landroid/database/Cursor;)Lorg/gnu/emacs/"
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"EmacsDirectoryEntry;");
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FIND_METHOD (open_document, "openDocument",
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"(Ljava/lang/String;Ljava/lang/String;ZZ)"
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"(Ljava/lang/String;Ljava/lang/String;ZZZ)"
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"Landroid/os/ParcelFileDescriptor;");
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FIND_METHOD (create_document, "createDocument",
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"(Ljava/lang/String;Ljava/lang/String;"
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@ -5590,7 +5590,7 @@ android_saf_file_open (struct android_vnode *vnode, int flags,
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struct android_saf_file_vnode *vp;
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jobject uri, id, descriptor;
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jmethodID method;
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jboolean trunc, write;
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jboolean read, trunc, write;
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jint fd;
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struct android_parcel_fd *info;
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struct stat statb;
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@ -5601,6 +5601,15 @@ android_saf_file_open (struct android_vnode *vnode, int flags,
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return -1;
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}
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/* O_APPEND isn't supported as a consequence of Android content
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providers defaulting to truncating the file. */
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if (flags & O_APPEND)
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{
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errno = EOPNOTSUPP;
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return -1;
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}
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/* Build strings for both the URI and ID. */
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vp = (struct android_saf_file_vnode *) vnode;
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@ -5611,18 +5620,43 @@ android_saf_file_open (struct android_vnode *vnode, int flags,
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vp->document_id);
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android_exception_check_1 (uri);
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/* Open a parcel file descriptor according to flags. */
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/* Open a parcel file descriptor according to flags. Documentation
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for the SAF openDocument operation is scant and seldom helpful.
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It's clear that their file access modes are inconsistently
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implemented, and that at least:
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r = either an FIFO or a real file, without truncation.
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w = either an FIFO or a real file, with truncation.
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wt = either an FIFO or a real file, with truncation.
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rw = a real file, without truncation.
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rwt = a real file, with truncation.
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This diverges from the self-contradicting documentation, where
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openDocument says nothing about truncation, and openFile, where
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w can elect not to truncate.
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Since Emacs is prepared to handle FIFOs within fileio.c, simply
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use the straightforward relationships possible. */
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method = service_class.open_document;
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trunc = (flags & O_TRUNC);
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write = (((flags & O_RDWR) == O_RDWR) || (flags & O_WRONLY));
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read = trunc = write = false;
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if ((flags & O_RDWR) == O_RDWR || (flags & O_WRONLY))
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write = true;
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if (flags & O_TRUNC)
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trunc = true;
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if ((flags & O_RDWR) == O_RDWR || !write)
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read = true;
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inside_saf_critical_section = true;
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descriptor
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= (*android_java_env)->CallNonvirtualObjectMethod (android_java_env,
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emacs_service,
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service_class.class,
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method, uri, id,
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write, trunc);
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read, write, trunc);
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inside_saf_critical_section = false;
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if (android_saf_exception_check (2, uri, id))
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@ -6448,6 +6482,8 @@ android_vfs_init (JNIEnv *env, jobject manager)
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vnodes may not be reentrant, but operating on them from within an
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async input handler will at worst cause an error to be returned.
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The eight is that some vnode types do not support O_APPEND.
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And the final drawback is that directories cannot be directly
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opened. Instead, `dirfd' must be called on a directory stream used
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by `openat'.
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