[PATCH] vmcore-dmesg: avoid allocating large memory chunk for log buf
Cong Wang
xiyou.wangcong at gmail.com
Tue Jun 27 09:43:33 PDT 2017
Ping... Any review?
On Mon, Jun 19, 2017 at 3:23 PM, Cong Wang <xiyou.wangcong at gmail.com> wrote:
> In kdump kernel, we got:
>
> Saving vmcore-dmesg.txt
> Failed to malloc 67108864 bytes for the logbuf: Cannot allocate memory
>
> Apparently 64M is too luxury for a kdump kernel which only has 128M
> in total.
>
> We can avoid allocating such a large memory chunk, instead just allocate
> a smaller chunk inside the loop each time.
>
> Verify the result by comparing the vmcore-dmesg output with and without
> this patch.
>
> Cc: Simon Horman <horms at verge.net.au>
> Signed-off-by: Cong Wang <xiyou.wangcong at gmail.com>
> ---
> vmcore-dmesg/vmcore-dmesg.c | 101 ++++++++++++++++++--------------------------
> 1 file changed, 41 insertions(+), 60 deletions(-)
>
> diff --git a/vmcore-dmesg/vmcore-dmesg.c b/vmcore-dmesg/vmcore-dmesg.c
> index a8f56df..593557c 100644
> --- a/vmcore-dmesg/vmcore-dmesg.c
> +++ b/vmcore-dmesg/vmcore-dmesg.c
> @@ -565,53 +565,12 @@ static inline uint64_t struct_val_u64(char *ptr, unsigned int offset)
> return(file64_to_cpu(*(uint64_t *)(ptr + offset)));
> }
>
> -/* human readable text of the record */
> -static char *log_text(char *msg)
> -{
> - return msg + log_sz;
> -}
> -
> -/* get record by index; idx must point to valid msg */
> -static char *log_from_idx(char *log_buf, uint32_t idx)
> -{
> - char *msg = log_buf + idx;
> -
> - /*
> - * A length == 0 record is the end of buffer marker. Wrap around and
> - * read the message at the start of the buffer.
> - */
> - if (!struct_val_u16(msg, log_offset_len))
> - return log_buf;
> - return msg;
> -}
> -
> -/* get next record; idx must point to valid msg */
> -static uint32_t log_next(char *log_buf, uint32_t idx)
> -{
> - char *msg = log_buf + idx;
> - uint16_t len;
> -
> - /* length == 0 indicates the end of the buffer; wrap */
> - /*
> - * A length == 0 record is the end of buffer marker. Wrap around and
> - * read the message at the start of the buffer as *this* one, and
> - * return the one after that.
> - */
> - len = struct_val_u16(msg, log_offset_len);
> - if (!len) {
> - msg = log_buf;
> - return struct_val_u16(msg, log_offset_len);
> - }
> - return idx + len;
> -}
> -
> /* Read headers of log records and dump accordingly */
> static void dump_dmesg_structured(int fd)
> {
> #define OUT_BUF_SIZE 4096
> uint64_t log_buf, log_buf_offset, ts_nsec;
> uint32_t log_first_idx, log_next_idx, current_idx, len = 0, i;
> - int log_buf_len;
> char *buf, out_buf[OUT_BUF_SIZE];
> ssize_t ret;
> char *msg;
> @@ -659,34 +618,33 @@ static void dump_dmesg_structured(int fd)
> }
>
> log_buf = read_file_pointer(fd, vaddr_to_offset(log_buf_vaddr));
> - log_buf_len = read_file_s32(fd, vaddr_to_offset(log_buf_len_vaddr));
>
> log_first_idx = read_file_u32(fd, vaddr_to_offset(log_first_idx_vaddr));
> log_next_idx = read_file_u32(fd, vaddr_to_offset(log_next_idx_vaddr));
>
> log_buf_offset = vaddr_to_offset(log_buf);
>
> - buf = calloc(1, log_buf_len);
> + buf = calloc(1, log_sz);
> if (!buf) {
> - fprintf(stderr, "Failed to malloc %d bytes for the logbuf:"
> - " %s\n", log_buf_len, strerror(errno));
> + fprintf(stderr, "Failed to malloc %" PRId64 " bytes for the log:"
> + " %s\n", log_sz, strerror(errno));
> exit(64);
> }
>
> - ret = pread(fd, buf, log_buf_len, log_buf_offset);
> - if (ret != log_buf_len) {
> - fprintf(stderr, "Failed to read log buffer of size %d bytes:"
> - " %s\n", log_buf_len, strerror(errno));
> - exit(65);
> - }
> -
> /* Parse records and write out data at standard output */
>
> current_idx = log_first_idx;
> len = 0;
> while (current_idx != log_next_idx) {
> - msg = log_from_idx(buf, current_idx);
> - ts_nsec = struct_val_u64(msg, log_offset_ts_nsec);
> + uint16_t loglen;
> +
> + ret = pread(fd, buf, log_sz, log_buf_offset + current_idx);
> + if (ret != log_sz) {
> + fprintf(stderr, "Failed to read log of size %" PRId64 " bytes:"
> + " %s\n", log_sz, strerror(errno));
> + exit(65);
> + }
> + ts_nsec = struct_val_u64(buf, log_offset_ts_nsec);
> imaxdiv_sec = imaxdiv(ts_nsec, 1000000000);
> imaxdiv_usec = imaxdiv(imaxdiv_sec.rem, 1000);
>
> @@ -695,9 +653,22 @@ static void dump_dmesg_structured(int fd)
> (long long unsigned int)imaxdiv_usec.quot);
>
> /* escape non-printable characters */
> - text_len = struct_val_u16(msg, log_offset_text_len);
> + text_len = struct_val_u16(buf, log_offset_text_len);
> + msg = calloc(1, text_len);
> + if (!msg) {
> + fprintf(stderr, "Failed to malloc %u bytes for log text:"
> + " %s\n", text_len, strerror(errno));
> + exit(64);
> + }
> +
> + ret = pread(fd, msg, text_len, log_buf_offset + current_idx + log_sz);
> + if (ret != text_len) {
> + fprintf(stderr, "Failed to read log text of size %u bytes:"
> + " %s\n", text_len, strerror(errno));
> + exit(65);
> + }
> for (i = 0; i < text_len; i++) {
> - unsigned char c = log_text(msg)[i];
> + unsigned char c = msg[i];
>
> if (!isprint(c) && !isspace(c))
> len += sprintf(out_buf + len, "\\x%02x", c);
> @@ -711,11 +682,21 @@ static void dump_dmesg_structured(int fd)
> }
>
> out_buf[len++] = '\n';
> -
> - /* Move to next record */
> - current_idx = log_next(buf, current_idx);
> + free(msg);
> + /* length == 0 indicates the end of the buffer; wrap */
> + /*
> + * A length == 0 record is the end of buffer marker. Wrap around and
> + * read the message at the start of the buffer as *this* one, and
> + * return the one after that.
> + */
> + loglen = struct_val_u16(buf, log_offset_len);
> + if (!loglen)
> + current_idx = log_first_idx;
> + else
> + /* Move to next record */
> + current_idx += loglen;
> }
> -
> + free(buf);
> if (len)
> write_to_stdout(out_buf, len);
> }
> --
> 2.5.5
>
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