[U-Boot] [PATCH v2 2/3] fs/fat: Improve error handling

Kyle Moffett
2011-12-21T17:08:11Z

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>

--

v2: No change

---
fs/fat/fat.c | 18 ++++++++++++++----
1 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/fs/fat/fat.c b/fs/fat/fat.c
index 9ceb3ec..afe486f 100644
--- a/fs/fat/fat.c
+++ b/fs/fat/fat.c
@@ -276,6 +276,8 @@ 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 +
@@ -286,16 +288,19 @@ 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;
@@ -804,6 +809,11 @@ 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 -
--
1.7.7.3