Re: [Qemu-devel] [PATCH v3] qga: Support enum names in guest-file-seek

[Michael Roth <mdroth@linux.vnet.ibm.com>]

Quoting Eric Blake (2016-02-09 15:27:16)
> Magic constants are a pain to use, especially when we run the
> risk that our choice of '1' for QGA_SEEK_CUR might differ from
> the host or guest's choice of SEEK_CUR.  Better is to use an
> enum value, via a qapi alternate type for back-compatibility.
> 
> With this,
>  {"command":"guest-file-seek", "arguments":{"handle":1,
>   "offset":0, "whence":"cur"}}
> becomes a synonym for the older
>  {"command":"guest-file-seek", "arguments":{"handle":1,
>   "offset":0, "whence":1}}
> 
> Signed-off-by: Eric Blake <eblake@redhat.com>

Reviewed-by: Michael Roth <mdroth@linux.vnet.ibm.com>

> 
> ---
> v2: rebase on top of qapi work
> ---
> v3: rebase to latest
> v2 was here: https://lists.gnu.org/archive/html/qemu-devel/2015-12/msg03565.html
> v1 was here: https://lists.gnu.org/archive/html/qemu-devel/2015-11/msg05730.html
> 
>  qga/guest-agent-core.h |  9 ++-------
>  qga/commands-posix.c   | 19 ++++++-------------
>  qga/commands-win32.c   | 19 ++++++-------------
>  qga/commands.c         | 21 +++++++++++++++++++++
>  tests/test-qga.c       |  9 ++++-----
>  qga/qapi-schema.json   | 33 +++++++++++++++++++++++++++++++--
>  6 files changed, 70 insertions(+), 40 deletions(-)
> 
> diff --git a/qga/guest-agent-core.h b/qga/guest-agent-core.h
> index 238dc6b..0a49516 100644
> --- a/qga/guest-agent-core.h
> +++ b/qga/guest-agent-core.h
> @@ -12,16 +12,10 @@
>   */
>  #include "qapi/qmp/dispatch.h"
>  #include "qemu-common.h"
> +#include "qga-qmp-commands.h"
> 
>  #define QGA_READ_COUNT_DEFAULT 4096
> 
> -/* Mapping of whence codes used by guest-file-seek. */
> -enum {
> -    QGA_SEEK_SET = 0,
> -    QGA_SEEK_CUR = 1,
> -    QGA_SEEK_END = 2,
> -};
> -
>  typedef struct GAState GAState;
>  typedef struct GACommandState GACommandState;
>  extern GAState *ga_state;
> @@ -44,6 +38,7 @@ void ga_set_frozen(GAState *s);
>  void ga_unset_frozen(GAState *s);
>  const char *ga_fsfreeze_hook(GAState *s);
>  int64_t ga_get_fd_handle(GAState *s, Error **errp);
> +int ga_parse_whence(GuestFileWhence *whence, Error **errp);
> 
>  #ifndef _WIN32
>  void reopen_fd_to_null(int fd);
> diff --git a/qga/commands-posix.c b/qga/commands-posix.c
> index 9589b2d..9f51fae 100644
> --- a/qga/commands-posix.c
> +++ b/qga/commands-posix.c
> @@ -550,31 +550,24 @@ GuestFileWrite *qmp_guest_file_write(int64_t handle, const char *buf_b64,
>  }
> 
>  struct GuestFileSeek *qmp_guest_file_seek(int64_t handle, int64_t offset,
> -                                          int64_t whence_code, Error **errp)
> +                                          GuestFileWhence *whence_code,
> +                                          Error **errp)
>  {
>      GuestFileHandle *gfh = guest_file_handle_find(handle, errp);
>      GuestFileSeek *seek_data = NULL;
>      FILE *fh;
>      int ret;
>      int whence;
> +    Error *err = NULL;
> 
>      if (!gfh) {
>          return NULL;
>      }
> 
>      /* We stupidly exposed 'whence':'int' in our qapi */
> -    switch (whence_code) {
> -    case QGA_SEEK_SET:
> -        whence = SEEK_SET;
> -        break;
> -    case QGA_SEEK_CUR:
> -        whence = SEEK_CUR;
> -        break;
> -    case QGA_SEEK_END:
> -        whence = SEEK_END;
> -        break;
> -    default:
> -        error_setg(errp, "invalid whence code %"PRId64, whence_code);
> +    whence = ga_parse_whence(whence_code, &err);
> +    if (err) {
> +        error_propagate(errp, err);
>          return NULL;
>      }
> 
> diff --git a/qga/commands-win32.c b/qga/commands-win32.c
> index cf0757c..2799f5f 100644
> --- a/qga/commands-win32.c
> +++ b/qga/commands-win32.c
> @@ -385,7 +385,8 @@ done:
>  }
> 
>  GuestFileSeek *qmp_guest_file_seek(int64_t handle, int64_t offset,
> -                                   int64_t whence_code, Error **errp)
> +                                   GuestFileWhence *whence_code,
> +                                   Error **errp)
>  {
>      GuestFileHandle *gfh;
>      GuestFileSeek *seek_data;
> @@ -394,6 +395,7 @@ GuestFileSeek *qmp_guest_file_seek(int64_t handle, int64_t offset,
>      off_pos.QuadPart = offset;
>      BOOL res;
>      int whence;
> +    Error *err = NULL;
> 
>      gfh = guest_file_handle_find(handle, errp);
>      if (!gfh) {
> @@ -401,18 +403,9 @@ GuestFileSeek *qmp_guest_file_seek(int64_t handle, int64_t offset,
>      }
> 
>      /* We stupidly exposed 'whence':'int' in our qapi */
> -    switch (whence_code) {
> -    case QGA_SEEK_SET:
> -        whence = SEEK_SET;
> -        break;
> -    case QGA_SEEK_CUR:
> -        whence = SEEK_CUR;
> -        break;
> -    case QGA_SEEK_END:
> -        whence = SEEK_END;
> -        break;
> -    default:
> -        error_setg(errp, "invalid whence code %"PRId64, whence_code);
> +    whence = ga_parse_whence(whence_code, &err);
> +    if (err) {
> +        error_propagate(errp, err);
>          return NULL;
>      }
> 
> diff --git a/qga/commands.c b/qga/commands.c
> index 5b56786..e091ee1 100644
> --- a/qga/commands.c
> +++ b/qga/commands.c
> @@ -473,3 +473,24 @@ done:
> 
>      return ge;
>  }
> +
> +/* Convert GuestFileWhence (either a raw integer or an enum value) into
> + * the guest's SEEK_ constants.  */
> +int ga_parse_whence(GuestFileWhence *whence, Error **errp)
> +{
> +    /* Exploit the fact that we picked values to match QGA_SEEK_*. */
> +    if (whence->type == QTYPE_QSTRING) {
> +        whence->type = QTYPE_QINT;
> +        whence->u.value = whence->u.name;
> +    }
> +    switch (whence->u.value) {
> +    case QGA_SEEK_SET:
> +        return SEEK_SET;
> +    case QGA_SEEK_CUR:
> +        return SEEK_CUR;
> +    case QGA_SEEK_END:
> +        return SEEK_END;
> +    }
> +    error_setg(errp, "invalid whence code %"PRId64, whence->u.value);
> +    return -1;
> +}
> diff --git a/tests/test-qga.c b/tests/test-qga.c
> index 993b007..4d7542e 100644
> --- a/tests/test-qga.c
> +++ b/tests/test-qga.c
> @@ -7,7 +7,6 @@
> 
>  #include "libqtest.h"
>  #include "config-host.h"
> -#include "qga/guest-agent-core.h"
> 
>  typedef struct {
>      char *test_dir;
> @@ -451,8 +450,8 @@ static void test_qga_file_ops(gconstpointer fix)
>      /* seek */
>      cmd = g_strdup_printf("{'execute': 'guest-file-seek',"
>                            " 'arguments': { 'handle': %" PRId64 ", "
> -                          " 'offset': %d, 'whence': %d } }",
> -                          id, 6, QGA_SEEK_SET);
> +                          " 'offset': %d, 'whence': '%s' } }",
> +                          id, 6, "set");
>      ret = qmp_fd(fixture->fd, cmd);
>      qmp_assert_no_error(ret);
>      val = qdict_get_qdict(ret, "return");
> @@ -544,8 +543,8 @@ static void test_qga_file_write_read(gconstpointer fix)
>      /* seek to 0 */
>      cmd = g_strdup_printf("{'execute': 'guest-file-seek',"
>                            " 'arguments': { 'handle': %" PRId64 ", "
> -                          " 'offset': %d, 'whence': %d } }",
> -                          id, 0, QGA_SEEK_SET);
> +                          " 'offset': %d, 'whence': '%s' } }",
> +                          id, 0, "set");
>      ret = qmp_fd(fixture->fd, cmd);
>      qmp_assert_no_error(ret);
>      val = qdict_get_qdict(ret, "return");
> diff --git a/qga/qapi-schema.json b/qga/qapi-schema.json
> index 01c9ee4..c21f308 100644
> --- a/qga/qapi-schema.json
> +++ b/qga/qapi-schema.json
> @@ -314,6 +314,34 @@
>    'data': { 'position': 'int', 'eof': 'bool' } }
> 
>  ##
> +# @QGASeek:
> +#
> +# Symbolic names for use in @guest-file-seek
> +#
> +# @set: Set to the specified offset (same effect as 'whence':0)
> +# @cur: Add offset to the current location (same effect as 'whence':1)
> +# @end: Add offset to the end of the file (same effect as 'whence':2)
> +#
> +# Since: 2.6
> +##
> +{ 'enum': 'QGASeek', 'data': [ 'set', 'cur', 'end' ] }
> +
> +##
> +# @GuestFileWhence:
> +#
> +# Controls the meaning of offset to @guest-file-seek.
> +#
> +# @value: Integral value (0 for set, 1 for cur, 2 for end), available
> +#         for historical reasons, and might differ from the host's or
> +#         guest's SEEK_* values (since: 0.15)
> +# @name: Symbolic name, and preferred interface
> +#
> +# Since: 2.6
> +##
> +{ 'alternate': 'GuestFileWhence',
> +  'data': { 'value': 'int', 'name': 'QGASeek' } }
> +
> +##
>  # @guest-file-seek:
>  #
>  # Seek to a position in the file, as with fseek(), and return the
> @@ -324,14 +352,15 @@
>  #
>  # @offset: bytes to skip over in the file stream
>  #
> -# @whence: 0 for SEEK_SET, 1 for SEEK_CUR, or 2 for SEEK_END
> +# @whence: Symbolic or numeric code for interpreting offset
>  #
>  # Returns: @GuestFileSeek on success.
>  #
>  # Since: 0.15.0
>  ##
>  { 'command': 'guest-file-seek',
> -  'data':    { 'handle': 'int', 'offset': 'int', 'whence': 'int' },
> +  'data':    { 'handle': 'int', 'offset': 'int',
> +               'whence': 'GuestFileWhence' },
>    'returns': 'GuestFileSeek' }
> 
>  ##
> -- 
> 2.5.0
>