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Avoid ppoll timeout if there is prefix data already ready to send #242

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Merged
marmarek merged 1 commit into from
Aug 5, 2026
+6 −2
Merged

Avoid ppoll timeout if there is prefix data already ready to send #242

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8 changes: 6 additions & 2 deletions libqrexec/process_io.c
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Original file line number Diff line number Diff line change
Expand Up @@ -124,6 +124,7 @@ int qrexec_process_io(const struct process_io_request *req,
struct timespec zero_timeout = { 0, 0 };
struct timespec normal_timeout = { 10, 0 };
struct prefix_data empty = { 0, 0 }, prefix = req->prefix_data;
bool have_vchan_buffer_space;

if (is_service && stderr_fd == -1) {
struct msg_header hdr = { .type = MSG_DATA_STDERR, .len = 0 };
Expand Down Expand Up @@ -276,7 +277,9 @@ int qrexec_process_io(const struct process_io_request *req,

fds[FD_STDOUT].fd = -1;
fds[FD_STDERR].fd = -1;
if (libvchan_buffer_space(vchan) > (int)sizeof(struct msg_header)) {
have_vchan_buffer_space =
libvchan_buffer_space(vchan) > (int)sizeof(struct msg_header);
if (have_vchan_buffer_space) {
if (prefix.len == 0 && stdout_fd >= 0) {
fds[FD_STDOUT].fd = stdout_fd;
fds[FD_STDOUT].events = POLLIN;
Expand All @@ -290,7 +293,8 @@ int qrexec_process_io(const struct process_io_request *req,
fds[FD_VCHAN].fd = libvchan_fd_for_select(vchan);
fds[FD_VCHAN].events = POLLIN;

if (!buffer_len(stdin_buf) && libvchan_data_ready(vchan) > 0)
if ((prefix.len && have_vchan_buffer_space) ||
(!buffer_len(stdin_buf) && libvchan_data_ready(vchan) > 0))
/* check for other FDs, but exit immediately */
ret = ppoll(fds, FD_NUM, &zero_timeout, &pollmask);
else
Expand Down