[PATCH v11 02/10] btrfs-progs: receive: dynamically allocate sctx->read_buf

Omar Sandoval
2021-09-01T17:01:56Z

From: Boris Burkov <boris@bur.io>

In send stream v2, write commands can now be an arbitrary size. For that
reason, we can no longer allocate a fixed array in sctx for read_cmd.
Instead, read_cmd dynamically allocates sctx->read_buf. To avoid
needless reallocations, we reuse read_buf between read_cmd calls by also
keeping track of the size of the allocated buffer in sctx->read_buf_sz.

We do the first allocation of the old default size at the start of
processing the stream, and we only reallocate if we encounter a command
that needs a larger buffer.

Signed-off-by: Boris Burkov <boris@bur.io>
---
common/send-stream.c | 55 ++++++++++++++++++++++++++++----------------
send.h | 2 +-
2 files changed, 36 insertions(+), 21 deletions(-)

diff --git a/common/send-stream.c b/common/send-stream.c
index cd5aa311..3d3585c3 100644
--- a/common/send-stream.c
+++ b/common/send-stream.c
@@ -35,11 +35,11 @@ struct btrfs_send_attribute {
};

struct btrfs_send_stream {
- char read_buf[BTRFS_SEND_BUF_SIZE];
+ char *read_buf;
+ size_t read_buf_sz;
int fd;

int cmd;
- struct btrfs_cmd_header *cmd_hdr;
struct btrfs_send_attribute cmd_attrs[BTRFS_SEND_A_MAX + 1];
u32 version;

@@ -111,11 +111,12 @@ static int read_cmd(struct btrfs_send_stream *sctx)
u32 pos;
u32 crc;
u32 crc2;
+ struct btrfs_cmd_header *cmd_hdr;
+ size_t buf_len;

memset(sctx->cmd_attrs, 0, sizeof(sctx->cmd_attrs));

- ASSERT(sizeof(*sctx->cmd_hdr) <= sizeof(sctx->read_buf));
- ret = read_buf(sctx, sctx->read_buf, sizeof(*sctx->cmd_hdr));
+ ret = read_buf(sctx, sctx->read_buf, sizeof(*cmd_hdr));
if (ret < 0)
goto out;
if (ret) {
@@ -124,18 +125,22 @@ static int read_cmd(struct btrfs_send_stream *sctx)
goto out;
}

- sctx->cmd_hdr = (struct btrfs_cmd_header *)sctx->read_buf;
- cmd = le16_to_cpu(sctx->cmd_hdr->cmd);
- cmd_len = le32_to_cpu(sctx->cmd_hdr->len);
-
- if (cmd_len + sizeof(*sctx->cmd_hdr) >= sizeof(sctx->read_buf)) {
- ret = -EINVAL;
- error("command length %u too big for buffer %zu",
- cmd_len, sizeof(sctx->read_buf));
- goto out;
+ cmd_hdr = (struct btrfs_cmd_header *)sctx->read_buf;
+ cmd_len = le32_to_cpu(cmd_hdr->len);
+ cmd = le16_to_cpu(cmd_hdr->cmd);
+ buf_len = sizeof(*cmd_hdr) + cmd_len;
+ if (sctx->read_buf_sz < buf_len) {
+ sctx->read_buf = realloc(sctx->read_buf, buf_len);
+ if (!sctx->read_buf) {
+ ret = -ENOMEM;
+ error("failed to reallocate read buffer for cmd");
+ goto out;
+ }
+ sctx->read_buf_sz = buf_len;
+ /* We need to reset cmd_hdr after realloc of sctx->read_buf */
+ cmd_hdr = (struct btrfs_cmd_header *)sctx->read_buf;
}
-
- data = sctx->read_buf + sizeof(*sctx->cmd_hdr);
+ data = sctx->read_buf + sizeof(*cmd_hdr);
ret = read_buf(sctx, data, cmd_len);
if (ret < 0)
goto out;
@@ -145,11 +150,12 @@ static int read_cmd(struct btrfs_send_stream *sctx)
goto out;
}

- crc = le32_to_cpu(sctx->cmd_hdr->crc);
- sctx->cmd_hdr->crc = 0;
+ crc = le32_to_cpu(cmd_hdr->crc);
+ /* in send, crc is computed with header crc = 0, replicate that */
+ cmd_hdr->crc = 0;

crc2 = crc32c(0, (unsigned char*)sctx->read_buf,
- sizeof(*sctx->cmd_hdr) + cmd_len);
+ sizeof(*cmd_hdr) + cmd_len);

if (crc != crc2) {
ret = -EINVAL;
@@ -524,19 +530,28 @@ int btrfs_read_and_process_send_stream(int fd,
goto out;
}

+ sctx.read_buf = malloc(BTRFS_SEND_BUF_SIZE_V1);
+ if (!sctx.read_buf) {
+ ret = -ENOMEM;
+ error("unable to allocate send stream read buffer");
+ goto out;
+ }
+ sctx.read_buf_sz = BTRFS_SEND_BUF_SIZE_V1;
+
while (1) {
ret = read_and_process_cmd(&sctx);
if (ret < 0) {
last_err = ret;
errors++;
if (max_errors > 0 && errors >= max_errors)
- goto out;
+ break;
} else if (ret > 0) {
if (!honor_end_cmd)
ret = 0;
- goto out;
+ break;
}
}
+ free(sctx.read_buf);

out:
if (last_err && !ret)
diff --git a/send.h b/send.h
index 8dd865ec..228928a0 100644
--- a/send.h
+++ b/send.h
@@ -33,7 +33,7 @@ extern "C" {
#define BTRFS_SEND_STREAM_MAGIC "btrfs-stream"
#define BTRFS_SEND_STREAM_VERSION 1

-#define BTRFS_SEND_BUF_SIZE SZ_64K
+#define BTRFS_SEND_BUF_SIZE_V1 SZ_64K
#define BTRFS_SEND_READ_SIZE (1024 * 48)

enum btrfs_tlv_type {
--
2.33.0