Hi Hans-Peter,
these changes were introduced recently and only to suppress newly
introduced warnings in gcc 8.1.
So, yes, line 3 does nothing, but in order to suppress the
warnings one has
to use the return value of snprintf somehow.
The way I read
https://gcc.gnu.org/onlinedocs/gcc-8.1.0/gcc/Warning-Options.html#Warning-Options
seems to suggest that somehow means to set the
terminating 0 of the snprintf() result
buffer with the return value of snprintf().
The background of APL_PATH_MAX = 4096 is that unfortunately
various #include
files under /usr/include (even on the same platform) define
PATH_MAX differently,
ranging from 128 to 4096. Therefore, even though the theoretical
path length can
become > 4096 the underlying file system will not be able to deal
with it and then
it makes no difference if a file system call fails due the path
being truncated or too long.
Best Regards,
/// Jürgen
On 05/25/2018 12:00 PM, Hans-Peter
Sorge wrote:
Hello Juergen,
in Quad_SVx.cc around line 570:
char filename[APL_PATH_MAX + 1];
int slen = snprintf(filename, APL_PATH_MAX, "%s/%s",
dirname, entry->d_name);
if (slen >= APL_PATH_MAX) filename[APL_PATH_MAX] = 0;
filename will be returned at most APL_PATH_MAX chars long including
\0-termination.
So line -3- will do nothing as filename[APL_PATH_MAX-1] is already '\0'
dirname is defined as char dirname[APL_PATH_MAX + 1];
Just as a sidestep: If dirname was set to APL_PATH_MAX characters +
final \0, then
the resulting filename will be filled with a truncated path (one char
less ),
the following '/' and d_name are being discarded, resulting in an
invalid filename .
Here is my take:
dirname is 4096+1 chars long
entry->d_name is 256 chars long
So the max length of filename could then be APL_PATH_MAX(%s)+ 1 (/) +
255 (%s) +1 (\0). -> 4353 bytes long.
snprintf strips the trailing \0s from the input and adds one.
// PATH + / + NAME + \0
enum { FN_MAX_LENGTH=APL_PATH_MAX +1 +255 +1};
char filename[FN_MAX_LENGTH ];
snprintf(filename,FN_MAX_LENGTH , "%s/%s", dirname,
entry->d_name);
Again, I did not dig deeper into the code/spec to find out whether the
maximum filename length
should be 4096+1 bytes, then dirname has to be 4k-256byte long ,
or whether the maximum filename length should be 4353 bytes.
Best regards
Hans-Peter
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