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Re: [Qemu-devel] [PATCH v6 08/11] dump: Add APIs to operate DataCache
From: |
Laszlo Ersek |
Subject: |
Re: [Qemu-devel] [PATCH v6 08/11] dump: Add APIs to operate DataCache |
Date: |
Tue, 07 Jan 2014 16:22:00 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20131118 Thunderbird/17.0.11 |
comments below
On 01/05/14 08:27, Qiao Nuohan wrote:
> DataCache is used to store data temporarily, then the data will be written to
> vmcore. These functions will be called later when writing data of page to
> vmcore.
>
> Signed-off-by: Qiao Nuohan <address@hidden>
> ---
> dump.c | 52
> +++++++++++++++++++++++++++++++++++++++++++++++++
> include/sysemu/dump.h | 9 ++++++++
> 2 files changed, 61 insertions(+), 0 deletions(-)
>
> diff --git a/dump.c b/dump.c
> index 1fae152..b4c40f2 100644
> --- a/dump.c
> +++ b/dump.c
> @@ -1088,6 +1088,58 @@ out:
> return ret;
> }
>
> +static void prepare_data_cache(DataCache *data_cache, DumpState *s)
> +{
> + data_cache->fd = s->fd;
> + data_cache->data_size = 0;
> + data_cache->buf_size = BUFSIZE_DATA_CACHE;
> + data_cache->buf = g_malloc0(BUFSIZE_DATA_CACHE);
> +}
> +
> +static int write_cache(DataCache *dc, bool flag_flatten, void *buf, size_t
> size)
> +{
> + /*
> + * check if the space is enough to cache data, if not, write the cached
> + * data to dc->fd and reset the buf
> + */
> + if (dc->data_size + size > dc->buf_size) {
> + if (write_buffer(dc->fd, flag_flatten, dc->offset, dc->buf,
> + dc->data_size) < 0) {
> + return -1;
> + }
> +
> + dc->offset += dc->data_size;
> + dc->data_size = 0;
> + }
> +
> + memcpy(dc->buf + dc->data_size, buf, size);
> + dc->data_size += size;
> +
> + return 0;
> +}
I think we should at least add a check ("if" or assert()) because the
passed-in "size" could be greater than all of the room we have in the
buffer (ie. size > dc->buf_size), and in that case we'd overflow the buffer.
Then,
> +
> +/* write the remaining data in dc->buf to dc->fd */
> +static int sync_data_cache(DataCache *dc, bool flag_flatten)
> +{
> + if (dc->data_size == 0) {
> + return 0;
> + }
> +
> + if (write_buffer(dc->fd, flag_flatten, dc->offset, dc->buf,
> + dc->data_size) < 0) {
> + return -1;
> + }
> +
> + dc->offset += dc->data_size;
> +
> + return 0;
> +}
Incrementing the offset here, but not resetting dc->data_size, seems
inconsistent. Do both or neither. Ideally, do both, and rebase
write_cache() on top of this (ie. when syncing is necessary, call
sync_data_cache() from write_cache()).
It doesn't cause problems as-is in the current patchset though.
> +
> +static void free_data_cache(DataCache *data_cache)
> +{
> + g_free(data_cache->buf);
> +}
> +
> static ram_addr_t get_start_block(DumpState *s)
> {
> GuestPhysBlock *block;
> diff --git a/include/sysemu/dump.h b/include/sysemu/dump.h
> index b5eaf8d..ab44af8 100644
> --- a/include/sysemu/dump.h
> +++ b/include/sysemu/dump.h
> @@ -36,6 +36,7 @@
> #define BUFSIZE_BITMAP (PAGE_SIZE)
> #define PFN_BUFBITMAP (CHAR_BIT * BUFSIZE_BITMAP)
> #define ARCH_PFN_OFFSET (0)
> +#define BUFSIZE_DATA_CACHE (PAGE_SIZE * 4)
>
> #define paddr_to_pfn(X, page_shift) \
> (((unsigned long long)(X) >> (page_shift)) - ARCH_PFN_OFFSET)
> @@ -140,6 +141,14 @@ typedef struct QEMU_PACKED KdumpSubHeader64 {
> uint64_t max_mapnr_64; /* header_version 6 and later */
> } KdumpSubHeader64;
>
> +typedef struct DataCache {
> + int fd; /* fd of the file where to write the cached data */
> + char *buf; /* buffer for cached data */
> + size_t buf_size; /* size of the buf */
> + size_t data_size; /* size of cached data in buf */
> + off_t offset; /* offset of the file */
> +} DataCache;
> +
> struct GuestPhysBlockList; /* memory_mapping.h */
> int cpu_get_dump_info(ArchDumpInfo *info,
> const struct GuestPhysBlockList *guest_phys_blocks);
>
I feel that stuff that depends on page size should be centralized
somehow. I can't describe it very well now, but I feel that having a
bunch of macros that open-code the page size as 4096, and using struct
members elsewhere (with dynamically set values) for the same purpose, is
a mess.
However that could be refactored in a separate series, *if* you think it
would be worthwhile.
Reviewed-by: Laszlo Ersek <address@hidden>
- [Qemu-devel] [PATCH v6 11/11] Add 'query-dump-guest-memory-capability' command, (continued)
- [Qemu-devel] [PATCH v6 11/11] Add 'query-dump-guest-memory-capability' command, Qiao Nuohan, 2014/01/05
- [Qemu-devel] [PATCH v6 02/11] dump: Add API to write header of flatten format, Qiao Nuohan, 2014/01/05
- [Qemu-devel] [PATCH v6 04/11] dump: Add API to write elf notes to buffer, Qiao Nuohan, 2014/01/05
- [Qemu-devel] [PATCH v6 10/11] dump: Make kdump-compressed format available for 'dump-guest-memory', Qiao Nuohan, 2014/01/05
- [Qemu-devel] [PATCH v6 08/11] dump: Add APIs to operate DataCache, Qiao Nuohan, 2014/01/05
- Re: [Qemu-devel] [PATCH v6 08/11] dump: Add APIs to operate DataCache,
Laszlo Ersek <=
- [Qemu-devel] [PATCH v6 09/11] dump: Add API to write dump pages, Qiao Nuohan, 2014/01/05
- [Qemu-devel] [PATCH v6 07/11] dump: Add API to write dump_bitmap, Qiao Nuohan, 2014/01/05
- [Qemu-devel] [PATCH v6 01/11] dump: Add argument to write_elfxx_notes, Qiao Nuohan, 2014/01/05
- Re: [Qemu-devel] [PATCH v6 00/11] Make 'dump-guest-memory' dump in kdump-compressed format, Qiao Nuohan, 2014/01/07