Re: pg_basebackup check vs Windows file path limits

On 2023-11-11 Sa 11:31, Alvaro Herrera wrote:
> On 2023-Jul-08, Andrew Dunstan wrote:
>
>> # Running: pg_basebackup -D C:\\tools\\nmsys64\\home\\pgrunner\\bf\\root\\REL_16_STABLE\\pgsql.build/testrun/pg_basebackup/010_pg_basebackup/data/t_010_pg_basebackup_main_data/backup/tarbackup2 -h C:/tools/nmsys64/tmp/63ohSgsh21 -p 54699 --checkpoint fast --no-sync -Ft
>> WARNING:  aborting backup due to backend exiting before pg_backup_stop was called
>> pg_basebackup: error: could not initiate base backup: ERROR:  could not get junction for "./pg_replslot": More data is available.
> Why not patch pgreadlink to use the method recommended by Microsoft,
> that DeviceIoControl() is called first with a NULL reparseBuffer to
> determine the size needed, then a second time with a buffer of that
> size?
>
> https://learn.microsoft.com/en-us/windows/win32/api/ioapiset/nf-ioapiset-deviceiocontrol


Hmm, here's what that page says - I can't see it saying what you're 
suggesting here - am I missing something?:


|[in] nOutBufferSize|

The size of the output buffer, in bytes.

|[out, optional] lpBytesReturned|

A pointer to a variable that receives the size of the data stored in the 
output buffer, in bytes.

If the output buffer is too small to receive any data, the call fails, 
GetLastError 
<https://learn.microsoft.com/en-us/windows/desktop/api/errhandlingapi/nf-errhandlingapi-getlasterror> 
returns *ERROR_INSUFFICIENT_BUFFER*, and /lpBytesReturned/ is zero.

If the output buffer is too small to hold all of the data but can hold 
some entries, some drivers will return as much data as fits. In this 
case, the call fails, GetLastError 
<https://learn.microsoft.com/en-us/windows/desktop/api/errhandlingapi/nf-errhandlingapi-getlasterror> 
returns *ERROR_MORE_DATA*, and /lpBytesReturned/ indicates the amount of 
data received. Your application should call *DeviceIoControl* again with 
the same operation, specifying a new starting point.



cheers


andrew

--
Andrew Dunstan
EDB:https://www.enterprisedb.com