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Allow xenstore watch
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@DemiMarie
DemiMarie committed Mar 11, 2023
1 parent 3a9a25f commit da47343
Showing 1 changed file with 58 additions and 21 deletions.
79 changes: 58 additions & 21 deletions not-script/not-script.c
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Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,7 @@
#include <linux/fs.h>

#include <xen/xen.h>
#include <xen/io/xenbus.h>
#include <xenstore.h>

static int open_file(const char *path) {
Expand All @@ -43,22 +44,30 @@ static int open_loop_dev(uint32_t devnum, bool writable)
return res == -1 ? -errno : res;
}

static bool use_autoclear(void) {
int const status = access("/etc/use-autoclear", F_OK);
if (!(status == 0 || (status == -1 && errno == ENOENT)))
err(1, "access(\"/etc/use-autoclear\")");
return status == 0;
}

static int setup_loop(struct loop_context *ctx,
uint32_t fd,
uint64_t offset,
uint64_t sizelimit,
bool writable) {
bool writable, bool autoclear) {
int dev_file = -1, status;

struct loop_config config = {
.fd = fd,
.block_size = 0, /* FIXME! */
.info = {
.lo_offset = offset,
.lo_sizelimit = sizelimit,
.lo_flags = LO_FLAGS_DIRECT_IO | (writable ? 0 : LO_FLAGS_READ_ONLY),
.lo_flags = LO_FLAGS_DIRECT_IO | (autoclear ? LO_FLAGS_AUTOCLEAR : 0) | (writable ? 0 : LO_FLAGS_READ_ONLY),
},
};

int dev_file = -1, status;
for (int retry_count = 0; retry_count < 5 /* arbitrary */; retry_count++) {
if ((status = ioctl(ctx->fd, LOOP_CTL_GET_FREE)) == -1)
return -errno;
Expand Down Expand Up @@ -86,7 +95,7 @@ static int setup_loop(struct loop_context *ctx,

static void
process_blk_dev(int fd, const char *path, bool writable, dev_t *dev,
uint64_t *diskseq, bool permissive)
uint64_t *diskseq, bool permissive, bool autoclear)
{
struct stat statbuf;
char buf[45];
Expand Down Expand Up @@ -143,7 +152,7 @@ process_blk_dev(int fd, const char *path, bool writable, dev_t *dev,
if (ctrl_fd < 0)
err(1, "open(/dev/loop-control)");
struct loop_context ctx = { .fd = ctrl_fd };
int loop_fd = setup_loop(&ctx, fd, 0, (uint64_t)statbuf.st_size, writable);
int loop_fd = setup_loop(&ctx, fd, 0, (uint64_t)statbuf.st_size, writable, autoclear);
if (loop_fd < 0)
err(1, "loop device setup failed");
if (dup3(loop_fd, fd, O_CLOEXEC) != fd)
Expand All @@ -169,7 +178,7 @@ process_blk_dev(int fd, const char *path, bool writable, dev_t *dev,
err(1, "ioctl(%d, BLKGETDISKSEQ, %p)", fd, diskseq);
}

static void validate_int_start(char **p, unsigned long *out)
static void validate_int_start(char **p, unsigned long *out, bool path)
{
char const s = **p;
if (s == '0') {
Expand All @@ -180,8 +189,10 @@ static void validate_int_start(char **p, unsigned long *out)
*out = strtoul(*p, p, 10);
if (errno)
err(1, "strtoul()");
} else if (path) {
errx(1, "Bad byte %d in XenStore path %s", s, *p);
} else {
errx(1, "Bad char '%c' in XenStore path %s", s, *p);
errx(1, "Bad byte %d at start of Xenbus state", s);
}
}

Expand Down Expand Up @@ -226,6 +237,9 @@ static void remove_device(struct xs_handle *const h, char *xenstore_path_buffer,
uint64_t actual_diskseq;
unsigned long _major, _minor;

if (use_autoclear())
return;

/*
* Order matters here: the kernel only cares about "physical-device" for
* now, so ensure that it gets removed first.
Expand Down Expand Up @@ -367,10 +381,10 @@ int main(int argc, char **argv)
/* strtoul() is not const-correct, sorry... */
char *xs_path_extra = (char *)(xs_path + (sizeof(BACKEND_VBD) - 1));
unsigned long peer_domid, tmp;
validate_int_start(&xs_path_extra, &peer_domid);
validate_int_start(&xs_path_extra, &peer_domid, true);
if (*xs_path_extra++ != '/')
errx(1, "Peer domain ID %lu not followed by '/'", peer_domid);
validate_int_start(&xs_path_extra, &tmp);
validate_int_start(&xs_path_extra, &tmp, true);
if (*xs_path_extra)
errx(1, "Junk after XenStore device ID %lu", tmp);
if (peer_domid >= DOMID_FIRST_RESERVED)
Expand Down Expand Up @@ -442,8 +456,9 @@ int main(int argc, char **argv)
if ((fd = open(data, (writable ? O_RDWR : O_RDONLY) | O_NOCTTY | O_CLOEXEC | O_NONBLOCK)) < 0)
err(1, "open(%s)", data);
char phys_dev[18], hex_diskseq[17];
bool const autoclear = use_autoclear();

process_blk_dev(fd, data, writable, &dev, &diskseq, permissive);
process_blk_dev(fd, data, writable, &dev, &diskseq, permissive, autoclear);
unsigned const int l =
(unsigned)snprintf(phys_dev, sizeof phys_dev, "%lx:%lx",
(unsigned long)major(dev), (unsigned long)minor(dev));
Expand All @@ -453,11 +468,12 @@ int main(int argc, char **argv)
if (snprintf(hex_diskseq, sizeof(hex_diskseq), "%016llx", (unsigned long long)diskseq) != 16)
err(1, "snprintf");

const char *watch_token = "state";
strcpy(extra_path, watch_token);

if (!xs_watch(h, xenstore_path_buffer, watch_token))
err(1, "Cannot setup XenStore watch on %s", xenstore_path_buffer);
if (autoclear) {
const char *watch_token = "state";
strcpy(extra_path, watch_token);
if (!xs_watch(h, xenstore_path_buffer, watch_token))
err(1, "Cannot setup XenStore watch on %s", xenstore_path_buffer);
}

for (;;) {
xs_transaction_t t = xs_transaction_start(h);
Expand All @@ -483,11 +499,32 @@ int main(int argc, char **argv)
err(1, "xs_transaction_end");
}

unsigned int num;
char **watch_res = xs_read_watch(h, &num);
if (!watch_res)
err(1, "xs_read_watch");

free(watch_res);
if (autoclear) {
strcpy(extra_path, "state");
for (;;) {
unsigned int num;
char **watch_res = xs_read_watch(h, &num);
if (!watch_res)
err(1, "xs_read_watch");
warnx("Xenstore watch for %s triggered", watch_res[0]);
free(watch_res);
unsigned int state_len = 0;
char *value = xs_read(h, 0, xenstore_path_buffer, &state_len);
if (!value) {
if (errno == ENOENT)
break;
err(1, "xs_read(\"%s\")", xenstore_path_buffer);
}
char *endptr = value;
unsigned long _xenbus_state;
validate_int_start(&endptr, &_xenbus_state, false);
if (endptr != value + state_len)
errx(1, "Invalid Xenbus state");
free(value);
warnx("Got Xenbus state %lu", _xenbus_state);
if (_xenbus_state > XenbusStateInitWait)
break;
}
}
xs_close(h);
}

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