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gossipd: make writes to gossip_store atomic.

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There's a corner case where otherwise a reader could see the header and
not the body of a message.  It could handle that in various ways,
but simplest (and most efficient) is to avoid it happening.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Rusty Russell
2019-06-04 03:43:25 +09:30
parent a5f6ef385a
commit 4399faf57c
1 changed files with 9 additions and 2 deletions
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11
gossipd/gossip_store.c
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@@ -1,5 +1,6 @@
#include "gossip_store.h"
#include <ccan/array_size/array_size.h>
#include <ccan/crc/crc.h>
#include <ccan/endian/endian.h>
#include <ccan/read_write_all/read_write_all.h>
@@ -12,6 +13,7 @@
#include <gossipd/gen_gossip_store.h>
#include <gossipd/gen_gossip_wire.h>
#include <stdio.h>
#include <sys/uio.h>
#include <unistd.h>
#include <wire/gen_peer_wire.h>
#include <wire/wire.h>
@@ -51,6 +53,7 @@ static bool append_msg(int fd, const u8 *msg, u64 *len)
{
beint32_t hdr[2];
u32 msglen;
struct iovec iov[2];
msglen = tal_count(msg);
hdr[0] = cpu_to_be32(msglen);
@@ -59,8 +62,12 @@ static bool append_msg(int fd, const u8 *msg, u64 *len)
if (len)
*len += sizeof(hdr) + msglen;
return (write(fd, hdr, sizeof(hdr)) == sizeof(hdr) &&
write(fd, msg, msglen) == msglen);
/* Use writev so it will appear in store atomically */
iov[0].iov_base = hdr;
iov[0].iov_len = sizeof(hdr);
iov[1].iov_base = (void *)msg;
iov[1].iov_len = msglen;
return writev(fd, iov, ARRAY_SIZE(iov)) == sizeof(hdr) + msglen;
}
struct gossip_store *gossip_store_new(struct routing_state *rstate)