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fs/fat: Improve error handling

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The FAT filesystem fails silently in inexplicable ways when given a
filesystem with a block-size that does not match the device sector size.
In theory this is not an unsupportable combination but requires a major
rewrite of a lot of the filesystem.  Until that occurs, the filesystem
should detect that scenario and display a helpful error message.

This scenario in particular occurred on a 512-byte blocksize FAT fs
stored in an El-Torito boot volume on a CD-ROM (2048-byte sector size).

Additionally, in many circumstances the ->block_read method will not
return a negative number to indicate an error but instead return 0 to
indicate the number of blocks successfully read (IE: None).

The FAT filesystem should defensively check to ensure that it got all of
the sectors that it asked for when reading.

Signed-off-by: Kyle Moffett <Kyle.D.Moffett@boeing.com>
This commit is contained in:
Kyle Moffett 2011-12-20 07:41:13 +00:00 • committed by Wolfgang Denk
parent 9813b750f3
commit 46236b1407
1 changed files with 14 additions and 4 deletions
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18
fs/fat/fat.c
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@ -274,6 +274,8 @@ get_cluster (fsdata *mydata, __u32 clustnum, __u8 *buffer,
{
__u32 idx = 0;
__u32 startsect;
__u32 nr_sect;
int ret;
if (clustnum > 0) {
startsect = mydata->data_begin +
@ -284,16 +286,19 @@ get_cluster (fsdata *mydata, __u32 clustnum, __u8 *buffer,
debug("gc - clustnum: %d, startsect: %d\n", clustnum, startsect);
if (disk_read(startsect, size / mydata->sect_size, buffer) < 0) {
debug("Error reading data\n");
nr_sect = size / mydata->sect_size;
ret = disk_read(startsect, nr_sect, buffer);
if (ret != nr_sect) {
debug("Error reading data (got %d)\n", ret);
return -1;
}
if (size % mydata->sect_size) {
__u8 tmpbuf[mydata->sect_size];
idx = size / mydata->sect_size;
if (disk_read(startsect + idx, 1, tmpbuf) < 0) {
debug("Error reading data\n");
ret = disk_read(startsect + idx, 1, tmpbuf);
if (ret != 1) {
debug("Error reading data (got %d)\n", ret);
return -1;
}
buffer += idx * mydata->sect_size;
@ -803,6 +808,11 @@ do_fat_read (const char *filename, void *buffer, unsigned long maxsize,
mydata->sect_size = (bs.sector_size[1] << 8) + bs.sector_size[0];
mydata->clust_size = bs.cluster_size;
if (mydata->sect_size != cur_part_info.blksz) {
printf("Error: FAT sector size mismatch (fs=%hu, dev=%lu)\n",
mydata->sect_size, cur_part_info.blksz);
return -1;
}
if (mydata->fatsize == 32) {
mydata->data_begin = mydata->rootdir_sect -