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btrfs-progs: fi mkswapfile: fix page count in header

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Per user report on https://old.reddit.com/r/btrfs/comments/107fnw1/btrfs_filesystem_mkswapfile_results_in_an/
the swapfile header does not contain the correct number of pages that
matches the file size and the activated swapfile is only 1GiB:

  # btrfs filesystem mkswapfile -s 10g swapfile
  # swapon swapfile
  # cat /proc/swaps
  Filename          Type    Size       Used    Priority
  /swap/swapfile    file    1048572    0       -2

A workaround is to run 'mkswap swapfile' before activation. Proper fix
is to calculate the number of (fixed size) 4K pages available for the
swap.

Issue: #568
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
David Sterba 2023-01-09 18:22:56 +01:00
parent 660d10d3fb
commit 54b90cb6e5
2 changed files with 34 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
Documentation/btrfs-filesystem.rst
View File

@ -190,7 +190,7 @@ label [<device>|<mountpoint>] [<newlabel>]
mkswapfile [-s size] file
Create a new file that's suitable and formatted as a swapfile. Default
size is 2GiB, minimum size is 40KiB.
size is 2GiB, fixed page size 4KiB, minimum size is 40KiB.
A swapfile must be created in a specific way: NOCOW and preallocated.
Subvolume containing a swapfile cannot be snapshotted and blocks of an
@ -200,6 +200,10 @@ mkswapfile [-s size] file
needs to be done by command ``swapon(8)``. See also command ``btrfs
inspect-internal map-swapfile`` and the :doc:`Swapfile feature<Swapfile>` description.
.. note::
The command is a simplified version of 'mkswap', if you want to set
label, page size, or other parameters please use 'mkswap' proper.
``Options``
-s|--size SIZE

40
cmds/filesystem.c
View File

@ -1449,26 +1449,26 @@ static const char * const cmd_filesystem_mkswapfile_usage[] = {
};
/*
* Swap signature in the first 4KiB, v2:
* Swap signature in the first 4KiB, v2, no label:
*
* 00000400 .. = 01 00 00 00 ff ff 03 00 00 00 00 00 cb 70 8e 60
* ^^^^^^^^^^^
* uuid 4B
* ^^^^^^^^^^^ ^^^^^^^^^^^
* page count 4B uuid 4B
* 00000420 .. = 1d fb 4e ca be d4 3f 1f 6a 6b 0c 03 00 00 00 00
* ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
* uuid 8B
* 00000ff0 .. = 00 00 00 00 00 00 53 57 41 50 53 50 41 43 45 32
* S W A P S P A C E 2
*/
static int write_swap_signature(int fd)
static int write_swap_signature(int fd, u32 page_count)
{
int ret;
static unsigned char swap[4096] = {
static unsigned char swap[SZ_4K] = {
[0x400] = 0x01,
[0x404] = 0xff,
[0x405] = 0xff,
[0x406] = 0x03,
/* 0x404 .. 0x407 number of pages (little-endian) */
/* 0x408 .. 0x40b number of bad pages (unused) */
/* 0x40c .. 0x42b UUID */
/* Last bytes of the page */
[0xff6] = 'S',
[0xff7] = 'W',
[0xff8] = 'A',
@ -1480,9 +1480,11 @@ static int write_swap_signature(int fd)
[0xffe] = 'E',
[0xfff] = '2',
};
u32 *pages = (u32 *)&swap[0x404];
*pages = cpu_to_le32(page_count);
uuid_generate(&swap[0x40c]);
ret = pwrite(fd, swap, 4096, 0);
ret = pwrite(fd, swap, SZ_4K, 0);
return ret;
}
@ -1494,6 +1496,7 @@ static int cmd_filesystem_mkswapfile(const struct cmd_struct *cmd, int argc, cha
const char *fname;
unsigned long flags;
u64 size = SZ_2G;
u64 page_count;
optind = 0;
while (1) {
@ -1545,7 +1548,22 @@ static int cmd_filesystem_mkswapfile(const struct cmd_struct *cmd, int argc, cha
ret = 1;
goto out;
}
pr_verbose(LOG_INFO, "fallocate to size %llu\n", size);
page_count = size / SZ_4K;
if (page_count <= 10) {
error("file too short");
ret = 1;
goto out;
}
/* First file page with header */
page_count--;
if (page_count > (u32)-1) {
error("file too big");
ret = 1;
goto out;
}
size = round_down(size, SZ_4K);
pr_verbose(LOG_INFO, "fallocate to size %llu, page size %u, %llu pages\n",
size, SZ_4K, page_count);
ret = fallocate(fd, 0, 0, size);
if (ret < 0) {
error("cannot fallocate file: %m");
@ -1553,7 +1571,7 @@ static int cmd_filesystem_mkswapfile(const struct cmd_struct *cmd, int argc, cha
goto out;
}
pr_verbose(LOG_INFO, "write swap signature\n");
ret = write_swap_signature(fd);
ret = write_swap_signature(fd, page_count);
if (ret < 0) {
error("cannot write swap signature: %m");
ret = 1;