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[PATCH] stat: don't explicitly request file size for filenames

From: Andreas Dilger
Subject: [PATCH] stat: don't explicitly request file size for filenames
Date: Wed, 3 Jul 2019 20:24:39 +0000

When calling 'stat -c %N' to print the filename, don't explicitly
request the size of the file via statx(), as it may add overhead on
some filesystems.  The size is only needed to optimize an allocation
for the relatively rare case of reading a symlink name, and the worst
effect is a somewhat-too-large temporary buffer may be allocated for
areadlink_with_size(), or internal retries if buffer is too small.

The file size will be returned by statx() on most filesystems, even
if not requested, unless the filesystem considers this to be too
expensive for that file, in which case the tradeoff is worthwhile.

* src/stat.c: Don't explicitly request STATX_SIZE for filenames.
Start with a 1KB buffer for areadlink_with_size() if st_size unset.
 src/stat.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/stat.c b/src/stat.c
index ec0bb7d..c887013 100644
--- a/src/stat.c
+++ b/src/stat.c
@@ -1282,7 +1282,7 @@ fmt_to_mask (char fmt)
   switch (fmt)
     case 'N':
-      return STATX_MODE|STATX_SIZE;
+      return STATX_MODE;
     case 'd':
     case 'D':
       return STATX_MODE;
@@ -1491,7 +1491,9 @@ print_stat (char *pformat, size_t prefix_len, unsigned 
int m,
       out_string (pformat, prefix_len, quoteN (filename));
       if (S_ISLNK (statbuf->st_mode))
-          char *linkname = areadlink_with_size (filename, statbuf->st_size);
+          /* if statx() didn't set size, most symlinks are under 1KB */
+          char *linkname = areadlink_with_size (filename, statbuf->st_size ?:
+                                                1023);
           if (linkname == NULL)
               error (0, errno, _("cannot read symbolic link %s"),

Cheers, Andreas
Andreas Dilger

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