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osmo_io: Document expectation that segmentation_cb() can modify msgb 

This is used for parsing e.g. the ipa header and setting msg->cb.
Guard against segmentation_cb changing msg->data in
iofd_handle_segmentation().

Change-Id: Idd2115baae98a7818aabb26232d4423d2d48fb5c
This commit is contained in:
Daniel Willmann 2023-07-07 11:17:59 +02:00 committed by laforge
parent a18f1d7be4
commit 7b59bab794
2 changed files with 13 additions and 4 deletions
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6
include/osmocom/core/osmo_io.h
View File

@ -46,7 +46,11 @@ struct osmo_io_ops {
* Needs to return the size of the next message. If it returns
* -EAGAIN or a value larger than msgb_length() (message is incomplete)
* osmo_io will wait for more data to be read. Other negative values
* cause the msg to be discarded. */
* cause the msg to be discarded.
* If a full message was received (segmentation_cb() returns a value <= msgb_length())
* the msgb will be trimmed to size by osmo_io and forwarded to the read call-back. Any
* parsing done to the msgb by segmentation_cb() will be preserved for the read_cb()
* (e.g. setting lxh or msgb->cb). */
int (*segmentation_cb)(struct msgb *msg);
};

11
src/core/osmo_io.c
View File

@ -226,6 +226,9 @@ static enum iofd_seg_act iofd_handle_segmentation(struct osmo_io_fd *iofd, struc
int extra_len, received_len;
struct msgb *msg_pending;
/* Save the start of message before segmentation_cb (which could change it) */
uint8_t *data = msg->data;
received_len = msgb_length(msg);
if (!iofd->io_ops.segmentation_cb) {
@ -258,12 +261,14 @@ static enum iofd_seg_act iofd_handle_segmentation(struct osmo_io_fd *iofd, struc
/* msgb contains more than one segment */
/* Copy the trailing data over */
msg_pending = iofd_msgb_alloc(iofd);
memcpy(msgb_data(msg_pending), msgb_data(msg) + expected_len, extra_len);
memcpy(msgb_data(msg_pending), data + expected_len, extra_len);
msgb_put(msg_pending, extra_len);
*pending_out = msg_pending;
/* Trim the original msgb to size */
msgb_trim(msg, expected_len);
/* Trim the original msgb to size. Don't use msgb_trim because we need to reference
* msg->data from before it might have been modified by the segmentation_cb(). */
msg->len = expected_len;
msg->tail = data + expected_len;
return IOFD_SEG_ACT_HANDLE_MORE;
defer: