Public bug reported:
I have an image of a broken FAT file system that contains approx. 30000
identically named files. These were created by a GPS logger, which
usually writes its track into a single file, but somehow managed to
create a new file each second due to a broken SD card.
To salvage the files, I use "dosfsck -aw file.img". That is initially
quite fast, renaming hundreds of files per second, but gets slower and
slower until renaming a single file takes multiple seconds.
The problem seems to be that the function auto_rename in in src/check.c
uses a loop to find an unused file name, starting with FSCK0000.000 and
incrementing to FSCK0000.001 and so on if the file name is already in
use. This is slow because, for each file, all the previous file names
are checked again (quadratic time).
I have solved the problem for me by using a random file name instead:
--- a/src/check.c
+++ b/src/check.c
@@ -384,7 +384,7 @@ static void auto_rename(DOS_FILE * file)
- number = 0;
+ number = random() % 10000000;
@@ -403,7 +403,7 @@ static void auto_rename(DOS_FILE * file)
- number++;
+ number = random() % 10000000;
I cancelled my first attempt of repairing the image after 12 hours. With
this patch, dosfsck was finished within 2 minutes.
** Affects: dosfstools (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1203568
Title:
dosfsck slow repairing thousands of identically named files
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