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mount: support the sizelimit and offset option for loop devices

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Starting with linux kernel v5.4 squashfs has a more strict parameter
checking implemented. Unlike util-linux mount, busybox never supported
the sizelimit option but simply forwards it to the kernel.
Since v5.4 mounting will fail with

    squashfs: Unknown parameter 'sizelimit'

Support the sizelimit parameter by setting it in the LOOP_SET_STATUS64
structure before handing it to the kernel.

While at it also add support for the offset option, which currently will
always be set to 0.

function                                             old     new   delta
cut_out_ull_opt                                        -     167    +167
singlemount                                         1230    1266     +36
set_loop                                             834     862     +28
losetup_main                                         479     483      +4
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 3/0 up/down: 235/0)             Total: 235 bytes

Signed-off-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Steffen Trumtrar
2020-07-29 10:43:53 +02:00
committed by Denys Vlasenko
parent abefc3c276
commit 6561e07460
4 changed files with 67 additions and 4 deletions
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4
libbb/loop.c
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@@ -102,7 +102,8 @@ int FAST_FUNC get_free_loop(void)
* search will re-use an existing loop device already bound to that
* file/offset if it finds one.
*/
int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offset, unsigned flags)
int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offset,
unsigned long long sizelimit, unsigned flags)
{
char dev[LOOP_NAMESIZE];
char *try;
@@ -185,6 +186,7 @@ int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offse
memset(&loopinfo, 0, sizeof(loopinfo));
safe_strncpy((char *)loopinfo.lo_file_name, file, LO_NAME_SIZE);
loopinfo.lo_offset = offset;
loopinfo.lo_sizelimit = sizelimit;
/*
* Used by mount to set LO_FLAGS_AUTOCLEAR.
* LO_FLAGS_READ_ONLY is not set because RO is controlled by open type of the file.