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Avoid reading the same sector multiple times in a row (!46)(#16) 

GParted internal file system detection is reading the same sector
multiple times in a row.  Add an optimisation to only read a sector if
it is different to the previously read sector.

Closes !46 - Whole device FAT32 file system reports device busy warning
             from mlabel
Closes #16 - "invalid argument for seek()" error on very small (<=40KiB)
             drives
This commit is contained in:
Mike Fleetwood 2019-07-12 10:09:50 +01:00 committed by Curtis Gedak
parent 5bb3415bcb
commit 869ebb71ea
1 changed files with 25 additions and 14 deletions
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23
src/GParted_Core.cc
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@ -1179,6 +1179,9 @@ FSType GParted_Core::detect_filesystem_internal(const Glib::ustring& path, Byte_
// * Apple File System Reference
// https://developer.apple.com/support/apple-file-system/Apple-File-System-Reference.pdf
Byte_Value prev_read_offset = -1;
memset(buf, 0, sector_size);
for ( unsigned int i = 0 ; i < sizeof( signatures ) / sizeof( signatures[0] ) ; i ++ )
{
const size_t len1 = std::min( ( signatures[i].sig1 == NULL ) ? 0U : strlen( signatures[i].sig1 ),
@ -1193,27 +1196,35 @@ FSType GParted_Core::detect_filesystem_internal(const Glib::ustring& path, Byte_
Byte_Value read_offset = signatures[i].offset1 / sector_size * sector_size;
memset(buf, 0, sector_size);
// Optimisation: only read new sector when it is different to the
// previously read sector.
if (read_offset != prev_read_offset)
{
if (lseek(fd, read_offset, SEEK_SET) == read_offset &&
read(fd, buf, sector_size) == sector_size )
{
prev_read_offset = read_offset;
}
else
{
// Outside block device boundaries or other error.
continue;
}
}
memcpy(magic1, buf + signatures[i].offset1 % sector_size, len1);
// WARNING: This assumes offset2 is in the same sector as offset1
if (signatures[i].sig2 != NULL)
{
memcpy(magic2, buf + signatures[i].offset2 % sector_size, len2);
}
if (memcmp(magic1, signatures[i].sig1, len1) == 0 &&
( signatures[i].sig2 == NULL ||
memcmp( magic2, signatures[i].sig2, len2 ) == 0 ) )
(signatures[i].sig2 == NULL || memcmp(magic2, signatures[i].sig2, len2) == 0) )
{
fstype = signatures[i].fstype;
break;
}
}
}
close(fd);
free( buf );