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walmethods.c/h: Make Walfile a struct, rather than a void *

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This makes the curent file position and pathname visible in a generic
way, so we no longer need current_walfile_name global variable or the
get_current_pos() method. Since that purported to be able to fail but
never actually did, this also lets us get rid of some unnecessary
error-handling code.

One risk of this change is that the get_current_pos() method
previously cleared the error indicator, and that will no longer happen
with the new approach. I looked for a way that this could cause problems
and did not find one.

The previous code was confused about whether "Walfile" was the
implementation-dependent structure representing a WAL file or
whether it was a pointer to that stucture. Some of the code used it
one way, and some in the other. The compiler tolerated that because
void * is interchangeable with void **, but now that Walfile is a
struct, it's necessary to be consistent. Hence, some references to
"Walfile" have been converted to "Walfile *".

Discussion: http://postgr.es/m/CA+TgmoZS0Kw98fOoAcGz8B9iDhdqB4Be4e=vDZaJZ5A-xMYBqA@mail.gmail.com
This commit is contained in:
Robert Haas
2022-09-19 11:20:18 -04:00
parent 1fe1d09652
commit 4fd1479494
3 changed files with 70 additions and 94 deletions
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27
src/bin/pg_basebackup/walmethods.h
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@@ -11,7 +11,20 @@
#include "common/compression.h"
typedef void *Walfile;
struct WalWriteMethod;
typedef struct WalWriteMethod WalWriteMethod;
typedef struct
{
off_t currpos;
char *pathname;
/*
* MORE DATA FOLLOWS AT END OF STRUCT
*
* Each WalWriteMethod is expected to embed this as the first member of
* a larger struct with method-specific fields following.
*/
} Walfile;
typedef enum
{
@@ -30,7 +43,6 @@ typedef enum
* care not to clobber errno between a failed method call and use of
* getlasterror() to retrieve the message.
*/
typedef struct WalWriteMethod WalWriteMethod;
struct WalWriteMethod
{
/*
@@ -39,13 +51,13 @@ struct WalWriteMethod
* automatically renamed in close(). If pad_to_size is specified, the file
* will be padded with NUL up to that size, if supported by the Walmethod.
*/
Walfile (*open_for_write) (const char *pathname, const char *temp_suffix, size_t pad_to_size);
Walfile *(*open_for_write) (const char *pathname, const char *temp_suffix, size_t pad_to_size);
/*
* Close an open Walfile, using one or more methods for handling automatic
* unlinking etc. Returns 0 on success, other values for error.
*/
int (*close) (Walfile f, WalCloseMethod method);
int (*close) (Walfile *f, WalCloseMethod method);
/* Check if a file exist */
bool (*existsfile) (const char *pathname);
@@ -66,15 +78,12 @@ struct WalWriteMethod
* Write count number of bytes to the file, and return the number of bytes
* actually written or -1 for error.
*/
ssize_t (*write) (Walfile f, const void *buf, size_t count);
/* Return the current position in a file or -1 on error */
off_t (*get_current_pos) (Walfile f);
ssize_t (*write) (Walfile *f, const void *buf, size_t count);
/*
* fsync the contents of the specified file. Returns 0 on success.
*/
int (*sync) (Walfile f);
int (*sync) (Walfile *f);
/*
* Clean up the Walmethod, closing any shared resources. For methods like