About signal handler install info
Dear All,
I want to know is there any method/API to know whether there is
previous signal handler for specific signal no.
Example:
In below case we install 3 handler. So my question is if before
calling signal (SIGUSR1, handler2); is there any way i can get info
that there is handler1 already install with SIGUSR1.
signal (SIGUSR1, handler1);
signal (SIGUSR1, handler2);
signal (SIGUSR1, handler3);
#include stdio.h
#include stdlib.h
#include pthread.h
#include signal.h
void *func ();
void handler1 ()
{
printf (\nIn handler 1\n);
}
void handler2 ()
{
printf (\nIn handler 2\n);
}
void handler3 ()
{ printf (\nIn handler 3\n); }
int main ()
{
int err=-1;
pthread_t t1,t2;
signal (SIGUSR1, handler1);
sleep(5);
signal (SIGUSR1, handler2);
sleep(5);
signal (SIGUSR1, handler3);
sleep(5);
pthread_create (t1, NULL, func, NULL);
sleep(20);
return 0;
}
void *func()
{
while (1) usleep(10);
}
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Re: About signal handler install info
See sigaction.
--- On Thu, 1/12/11, naveen yadav yad.nav...@gmail.com wrote:
From: naveen yadav yad.nav...@gmail.com
Subject: About signal handler install info
To: Kernelnewbies@kernelnewbies.org, kernelnewb...@nl.linux.org
Date: Thursday, 1 December, 2011, 3:33 PM
Dear All,
I want to know is there any method/API to know
whether there is
previous signal handler for specific signal no.
Example:
In below case we install 3 handler. So my question is
if before
calling signal (SIGUSR1, handler2); is there any way i can
get info
that there is handler1 already install with SIGUSR1.
signal (SIGUSR1, handler1);
signal (SIGUSR1, handler2);
signal (SIGUSR1, handler3);
#include stdio.h
#include stdlib.h
#include pthread.h
#include signal.h
void *func ();
void handler1 ()
{
printf (\nIn handler 1\n);
}
void handler2 ()
{
printf (\nIn handler 2\n);
}
void handler3 ()
{ printf (\nIn handler 3\n); }
int main ()
{
int err=-1;
pthread_t t1,t2;
signal (SIGUSR1, handler1);
sleep(5);
signal (SIGUSR1, handler2);
sleep(5);
signal (SIGUSR1, handler3);
sleep(5);
pthread_create (t1, NULL,
func, NULL);
sleep(20);
return 0;
}
void *func()
{
while (1) usleep(10);
}
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Re: Booting root filesystem from usb device
--- El mié 30-nov-11, Greg KH g...@kroah.com escribió: Then just pass the command line option to sleep for a while before looking for the root device. I do that just fine on my tiny dns server that runs from a USB flash drive. Look in Documentation/kernel-parameters.txt for the rootdelay= option for more details as to what to do. It worked like a charm. Looking at kernel-parameters.txt, I also came across rootwait option. If someone reads this and is trying something similar (using lilo) you may find this useful: http://lkml.indiana.edu/hypermail/linux/kernel/1105.2/03866.html Thanks, Ezequiel. ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: VFAT i_pos value
Kai Meyer k...@gnukai.com writes: I'm getting this error: FAT: Filesystem error (dev sblsnap0) fat_get_cluster: invalid cluster chain (i_pos 523791) I'm wondering if there was a way to figure out what sector is causing the error? I would like to try and track down what is changing that sector and fix the problem. Is there a straight forward way to convert i_pos to a sector value? I've been staring at the fat.c and fat.h code all morning, and I'm having trouble grok'ing the flow. The i_pos means directory entry (contains inode information in unix-fs) position, block number == i_pos / (logical-blocksize / 32) offset == i_pos (logical-blocksize / 32) the above position's directory entry contains information for problematic file. This is how to use i_pos information. FWIW, in this error case, the cluster chain in FAT table which is pointed by that entry, it has invalid cluster value. Thanks. -- OGAWA Hirofumi hirof...@mail.parknet.co.jp ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: VFAT i_pos value
On 12/01/2011 07:38 AM, OGAWA Hirofumi wrote: Kai Meyerk...@gnukai.com writes: I'm getting this error: FAT: Filesystem error (dev sblsnap0) fat_get_cluster: invalid cluster chain (i_pos 523791) I'm wondering if there was a way to figure out what sector is causing the error? I would like to try and track down what is changing that sector and fix the problem. Is there a straight forward way to convert i_pos to a sector value? I've been staring at the fat.c and fat.h code all morning, and I'm having trouble grok'ing the flow. The i_pos means directory entry (contains inode information in unix-fs) position, block number == i_pos / (logical-blocksize / 32) offset == i_pos (logical-blocksize / 32) the above position's directory entry contains information for problematic file. This is how to use i_pos information. FWIW, in this error case, the cluster chain in FAT table which is pointed by that entry, it has invalid cluster value. Thanks. If you would verify my math for me, I would appreciate it. In this case, my logical block size is 4096, because byte 13 of the 8Gb file system is 8, and I take that to be 8 * 512, which is 4096. So: block_number = 523791 / (4096 / 32) = 4092 offset = 523791 % (4096 / 32) = 15 // I assume you meant modulo in your original post, and not binary AND. So if the block_number is 4092, I would multiply that by 8 (sectors per logical block) to get the sector number: 32736 Does the error indicate that sector contains the corrupted data? Or is it the sector that contains the information that points to the corrupted data? Or is it something entirely different? -Kai Meyer ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Understanding kmap/kunmap
I want to be able to copy data into a struct bio *, so I use
bio_for_each_segment to loop through each bvec, like so:
void some_function(struct bio *bio, char *some_data) {
struct bio_vec *bvec;
int i;
unsigned int bio_so_far = 0;
bio_for_each_segment(bvec, bio, i) {
char *bio_buffer = __bio_kmap_atomic(bio, i, KM_USER0);
memcpy(bio_buffer, some_data + bio_so_far, bvec-bv_len);
__bio_kunmap_atomic(bio, KM_USER0);
bio_so_far += bvec-bv_len;
}
}
There's lots more to the function, but this is basically the distilled
version with out any extra stuff.
What I'm finding is that when the bio has multiple bvecs that share the
same page, only the first bvec's data actually gets copied back up to
user-space, the rest is garbage or null (meaning, what was there
already). For instance, I see a lot of bios from vfat that are 4096
bytes long but are comprised of 8 bvecs that are 512 bytes long that all
have an offset to the same page.
I've tried doing just one kmap_atomic on the page by keeping track of
what the last page I kmap'ed was, but that didn't fix the problem either.
Any documentation or high level explanation of kmap/kunmap or other
ideas to try are welcome.
-Kai Meyer
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Re: VFAT i_pos value
Kai Meyer k...@gnukai.com writes: The i_pos means directory entry (contains inode information in unix-fs) position, block number == i_pos / (logical-blocksize / 32) offset == i_pos (logical-blocksize / 32) the above position's directory entry contains information for problematic file. This is how to use i_pos information. FWIW, in this error case, the cluster chain in FAT table which is pointed by that entry, it has invalid cluster value. Thanks. If you would verify my math for me, I would appreciate it. In this case, my logical block size is 4096, because byte 13 of the 8Gb file system is 8, and I take that to be 8 * 512, which is 4096. So: block_number = 523791 / (4096 / 32) = 4092 offset = 523791 % (4096 / 32) = 15 // I assume you meant modulo in your original post, and not binary AND. Whoops, you are right. (I forgot -1) So if the block_number is 4092, I would multiply that by 8 (sectors per logical block) to get the sector number: 32736 Right. Does the error indicate that sector contains the corrupted data? No. Or is it the sector that contains the information that points to the corrupted data? Right. The i_pos is pointing a directory entry (include/linux/msdos_fs.h: struct msdos_dir_entry). And starthi (if FAT32) and start contain the pointer to next cluster number. That message was outputted when walking in cluster chain. If you want to see actual corrupted data, you can check the cluster chain by pointing from that directory entry. Thanks. -- OGAWA Hirofumi hirof...@mail.parknet.co.jp ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: Understanding kmap/kunmap
Correction. The problem occurs when 8 bios of size 512 with 1 bvec each
all share the same page. I made a bad assumption previously.
-Kai Meyer
On 12/01/2011 10:49 AM, Kai Meyer wrote:
I want to be able to copy data into a struct bio *, so I use
bio_for_each_segment to loop through each bvec, like so:
void some_function(struct bio *bio, char *some_data) {
struct bio_vec *bvec;
int i;
unsigned int bio_so_far = 0;
bio_for_each_segment(bvec, bio, i) {
char *bio_buffer = __bio_kmap_atomic(bio, i, KM_USER0);
memcpy(bio_buffer, some_data + bio_so_far, bvec-bv_len);
__bio_kunmap_atomic(bio, KM_USER0);
bio_so_far += bvec-bv_len;
}
}
There's lots more to the function, but this is basically the distilled
version with out any extra stuff.
What I'm finding is that when the bio has multiple bvecs that share the
same page, only the first bvec's data actually gets copied back up to
user-space, the rest is garbage or null (meaning, what was there
already). For instance, I see a lot of bios from vfat that are 4096
bytes long but are comprised of 8 bvecs that are 512 bytes long that all
have an offset to the same page.
I've tried doing just one kmap_atomic on the page by keeping track of
what the last page I kmap'ed was, but that didn't fix the problem either.
Any documentation or high level explanation of kmap/kunmap or other
ideas to try are welcome.
-Kai Meyer
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Re: VFAT i_pos value
On 12/01/2011 12:20 PM, OGAWA Hirofumi wrote:
Kai Meyerk...@gnukai.com writes:
The i_pos means directory entry (contains inode information in unix-fs)
position,
block number == i_pos / (logical-blocksize / 32)
offset == i_pos (logical-blocksize / 32)
the above position's directory entry contains information for
problematic file. This is how to use i_pos information.
FWIW, in this error case, the cluster chain in FAT table which is
pointed by that entry, it has invalid cluster value.
Thanks.
If you would verify my math for me, I would appreciate it.
In this case, my logical block size is 4096, because byte 13 of the 8Gb
file system is 8, and I take that to be 8 * 512, which is 4096. So:
block_number = 523791 / (4096 / 32) = 4092
offset = 523791 % (4096 / 32) = 15 // I assume you meant modulo in your
original post, and not binary AND.
Whoops, you are right. (I forgot -1)
So if the block_number is 4092, I would multiply that by 8 (sectors per
logical block) to get the sector number:
32736
Right.
Does the error indicate that sector contains the corrupted data?
No.
Or is it the sector that contains the information that points to the
corrupted data?
Right.
The i_pos is pointing a directory entry (include/linux/msdos_fs.h:
struct msdos_dir_entry).
And starthi (if FAT32) and start contain the pointer to next cluster
number. That message was outputted when walking in cluster chain.
If you want to see actual corrupted data, you can check the cluster
chain by pointing from that directory entry.
Thanks.
Thanks for the helpful response. I'm not entirely sure I understand the
next part though. I hacked a dirty entry dumper tool:
#include stdio.h
#include linux/msdos_fs.h
#include sys/types.h
#include sys/stat.h
#include fcntl.h
#include unistd.h
#include string.h
int main(int argc, char** argv)
{
off_t pos = atoi(argv[2]);
unsigned long block;
off_t sector;
unsigned int offset;
int fd = open(argv[1], O_RDONLY);
char buf[512];
struct msdos_dir_entry dirent;
block = pos / (4096 / 32);
sector = block * 8;
offset = pos % (4096 / 32);
printf(block %lu, sector %lu, offset %u\n, block, sector,
offset);
lseek(fd, sector * 512, SEEK_SET);
if (read(fd, buf, 512) 0) {
fprintf(stderr, Unable to read from device %s\n,
argv[1]);
return -1;
}
memcpy(dirent, buf + offset, sizeof(dirent));
printf(name %s\n, dirent.name);
printf(attr %u\n, dirent.attr);
printf(lcase %u\n, dirent.lcase);
printf(ctime_cs %u\n, dirent.ctime_cs);
printf(ctime %u\n, dirent.ctime);
printf(cdate %u\n, dirent.cdate);
printf(adate %u\n, dirent.adate);
printf(starthi %u\n, dirent.starthi);
printf(time %u\n, dirent.time);
printf(date %u\n, dirent.date);
printf(start %u\n, dirent.start);
printf(size %u\n, dirent.size);
}
Here's what it outputs:
./vfat_entry /dev/sblsnap0 523793
block 4092, sector 32736, offset 17
name
attr 255
lcase 255
ctime_cs 255
ctime 12799
cdate 12670
adate 8224
starthi 8224
time 23072
date 21061
start 32
size 2171155456
So, I take starthi, and shift 16 bits left, then and in the start value.
That should give me the byte address of the first cluster of the file,
correct?
Then I need to follow the cluster chain until I get a bad value.
Thanks
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Re: contribute to linux kernel
Hi all, i have downloaded the linux kernel 2.6 from git.I have seen the you tube video of how to modify and submit a patch to the linux kernel.I want to know how should i get which projects i can contribute.I have failry good knowledge of embedded linux,c,c++,etc. Can any one guide me how can i effectively contribute to linux kernel. Thanks and Regards, Mayank On Tue, Nov 15, 2011 at 4:05 AM, Mayank Agarwal mayank77fromin...@gmail.com wrote: Hi all, I have just joined the kernelnewbies.I want to contribute to linux kernel or to any of the open source ongoing projects.Has good experience in c,c++ and linux programming. Please suggest how can i go about that. Regards, Mayank ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
