[Libguestfs] [PATCH nbdkit 1/5] floppy: support FAT FSes with unused space.
Richard W.M. Jones
rjones at redhat.com
Wed Jun 16 16:15:40 UTC 2021
From: Nolan Leake <nolan at sigbus.net>
This is useful for at least 2 use cases:
- Testing support for non-full filesystem
- In conjuction with the CoW plugin, for making a writable
filesystem.
There is also a small bugfix, the partition bootsector didn't account
for the 2048 sector offset to the start of the partition when
calculating the number of sectors in the partition.
Signed-off-by: Nolan Leake <nolan at sigbus.net>
---
plugins/floppy/virtual-floppy.h | 2 ++
plugins/floppy/floppy.c | 9 ++++++-
plugins/floppy/virtual-floppy.c | 43 +++++++++++++++++++++++++++------
3 files changed, 46 insertions(+), 8 deletions(-)
diff --git a/plugins/floppy/virtual-floppy.h b/plugins/floppy/virtual-floppy.h
index e5e1e3c9..b3eac24e 100644
--- a/plugins/floppy/virtual-floppy.h
+++ b/plugins/floppy/virtual-floppy.h
@@ -198,6 +198,7 @@ struct virtual_floppy {
uint64_t fat_clusters; /* Size of FAT (clusters on disk). */
uint64_t data_size; /* Size of data region (bytes). */
uint64_t data_clusters; /* Size of data region (clusters). */
+ uint64_t data_used_clusters; /* Size of the used part of the data region. */
/* The disk layout:
* sector 0: MBR
@@ -229,6 +230,7 @@ struct virtual_floppy {
extern void init_virtual_floppy (struct virtual_floppy *floppy)
__attribute__((__nonnull__ (1)));
extern int create_virtual_floppy (const char *dir, const char *label,
+ uint64_t size,
struct virtual_floppy *floppy)
__attribute__((__nonnull__ (1, 2, 3)));
extern void free_virtual_floppy (struct virtual_floppy *floppy)
diff --git a/plugins/floppy/floppy.c b/plugins/floppy/floppy.c
index 3f5220b2..24850300 100644
--- a/plugins/floppy/floppy.c
+++ b/plugins/floppy/floppy.c
@@ -50,6 +50,9 @@ static char *dir = NULL;
/* Volume label. */
static const char *label = "NBDKITFLOPY";
+/* Filesystem size. */
+static uint64_t size = 0;
+
/* Virtual floppy. */
static struct virtual_floppy floppy;
@@ -82,6 +85,10 @@ floppy_config (const char *key, const char *value)
else if (strcmp (key, "label") == 0) {
label = value;
}
+ else if (strcmp (key, "size") == 0) {
+ if (nbdkit_parse_uint64_t ("size", value, &size) == -1)
+ return -1;
+ }
else {
nbdkit_error ("unknown parameter '%s'", key);
return -1;
@@ -109,7 +116,7 @@ floppy_config_complete (void)
static int
floppy_get_ready (void)
{
- return create_virtual_floppy (dir, label, &floppy);
+ return create_virtual_floppy (dir, label, size, &floppy);
}
static void *
diff --git a/plugins/floppy/virtual-floppy.c b/plugins/floppy/virtual-floppy.c
index 60916fc5..2d5fe72d 100644
--- a/plugins/floppy/virtual-floppy.c
+++ b/plugins/floppy/virtual-floppy.c
@@ -85,11 +85,12 @@ init_virtual_floppy (struct virtual_floppy *floppy)
}
int
-create_virtual_floppy (const char *dir, const char *label,
+create_virtual_floppy (const char *dir, const char *label, uint64_t size,
struct virtual_floppy *floppy)
{
size_t i;
uint64_t nr_bytes, nr_clusters;
+ uint64_t data_used_size;
uint32_t cluster;
if (visit (dir, floppy) == -1)
@@ -112,14 +113,14 @@ create_virtual_floppy (const char *dir, const char *label,
* The first cluster number is always 2 (0 and 1 are reserved), and
* (in this implementation) always contains the root directory.
*/
- floppy->data_size = 0;
+ data_used_size = 0;
cluster = 2;
for (i = 0; i < floppy->dirs.size; ++i) {
floppy->dirs.ptr[i].first_cluster = cluster;
nr_bytes =
ROUND_UP (floppy->dirs.ptr[i].table.size * sizeof (struct dir_entry),
CLUSTER_SIZE);
- floppy->data_size += nr_bytes;
+ data_used_size += nr_bytes;
nr_clusters = nr_bytes / CLUSTER_SIZE;
if (cluster + nr_clusters > UINT32_MAX)
goto too_big;
@@ -129,7 +130,7 @@ create_virtual_floppy (const char *dir, const char *label,
for (i = 0; i < floppy->files.size; ++i) {
floppy->files.ptr[i].first_cluster = cluster;
nr_bytes = ROUND_UP (floppy->files.ptr[i].statbuf.st_size, CLUSTER_SIZE);
- floppy->data_size += nr_bytes;
+ data_used_size += nr_bytes;
nr_clusters = nr_bytes / CLUSTER_SIZE;
if (cluster + nr_clusters > UINT32_MAX)
goto too_big;
@@ -137,7 +138,21 @@ create_virtual_floppy (const char *dir, const char *label,
cluster += nr_clusters;
}
+ if (size > 0) {
+ uint64_t data_size = size - (2080 * SECTOR_SIZE);
+ data_size = data_size - 2 * DIV_ROUND_UP((data_size / CLUSTER_SIZE + 2) * 4,
+ CLUSTER_SIZE) * CLUSTER_SIZE;
+ if (data_used_size > data_size) {
+ nbdkit_error ("filesystem is larger than \"size\" bytes");
+ return -1;
+ }
+ floppy->data_size = data_size;
+ } else {
+ floppy->data_size = data_used_size;
+ }
+
floppy->data_clusters = floppy->data_size / CLUSTER_SIZE;
+ floppy->data_used_clusters = data_used_size / CLUSTER_SIZE;
/* Despite its name, FAT32 only allows 28 bit cluster numbers, so
* give an error if we go beyond this.
@@ -199,6 +214,10 @@ create_virtual_floppy (const char *dir, const char *label,
if (create_regions (floppy) == -1)
return -1;
+ /* Check that if a size was specified, we ended up with it. */
+ if (size > 0)
+ assert (virtual_size (&floppy->regions) == size);
+
return 0;
}
@@ -488,7 +507,7 @@ create_partition_boot_sector (const char *label, struct virtual_floppy *floppy)
floppy->bootsect.sectors_per_track = htole16 (0);
floppy->bootsect.nr_heads = htole16 (0);
floppy->bootsect.nr_hidden_sectors = htole32 (0);
- floppy->bootsect.nr_sectors = htole32 (floppy->data_last_sector + 1);
+ floppy->bootsect.nr_sectors = htole32 (floppy->data_last_sector - 2048 + 1);
floppy->bootsect.sectors_per_fat =
htole32 (floppy->fat_clusters * SECTORS_PER_CLUSTER);
@@ -524,8 +543,9 @@ create_fsinfo (struct virtual_floppy *floppy)
floppy->fsinfo.signature2[1] = 0x72;
floppy->fsinfo.signature2[2] = 0x41;
floppy->fsinfo.signature2[3] = 0x61;
- floppy->fsinfo.free_data_clusters = htole32 (0);
- floppy->fsinfo.last_free_cluster = htole32 (2 + floppy->data_clusters);
+ floppy->fsinfo.free_data_clusters = htole32 (floppy->data_clusters -
+ floppy->data_used_clusters);
+ floppy->fsinfo.last_free_cluster = htole32 (2 + floppy->data_used_clusters);
floppy->fsinfo.signature3[0] = 0x00;
floppy->fsinfo.signature3[1] = 0x00;
floppy->fsinfo.signature3[2] = 0x55;
@@ -687,6 +707,15 @@ create_regions (struct virtual_floppy *floppy)
return -1;
}
+ /* Append region for empty data region if we have extra space. */
+ if (floppy->data_used_clusters != floppy->data_clusters) {
+ uint64_t clusters = (floppy->data_clusters - floppy->data_used_clusters);
+ if (append_region_len (&floppy->regions, "data padding",
+ clusters * CLUSTER_SIZE, 0, CLUSTER_SIZE,
+ region_zero) == -1)
+ return -1;
+ }
+
nbdkit_debug ("floppy: %zu regions, "
"total disk size %" PRIi64,
nr_regions (&floppy->regions),
--
2.32.0
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